Sacroiliac fusion system

ABSTRACT

A method of performing an orthopedic procedure in the sacroiliac region. At least one aperture is formed that at least partially extends through at least one of an ilium and a sacrum. An undercutting system is at least partially inserted into the aperture. The undercutting system includes an insertion apparatus, a probe assembly and a cutting assembly. The probe assembly is moved with respect to the insertion apparatus from a retracted position to an extended position. The probe assembly is manipulated within a joint between the ilium and the sacrum while the probe assembly is in the extended position. The cutting assembly is moved with respect to the insertion apparatus from a retracted position to an extended position. The cutting assembly is sharper than the probe assembly. The cutting assembly is manipulated within the joint between the ilium and the sacrum while the cutting assembly is in the extended position to form a fusion region. The undercutting system is removed from the aperture.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.13/465,612, which was filed on May 7, 2012, which is acontinuation-in-part of U.S. application Ser. No. 12/938,976, which wasfiled on Nov. 3, 2010, which claims the benefit of priority fromApplication Ser. No. 61/292,021, filed Jan. 4, 2010. This applicationclaims the benefit of priority from Application Ser. No. 61/610,759,filed Mar. 14, 2012, and Application Ser. No. 61/482,899, filed May 5,2011. The entire content of these U.S. applications are incorporatedherein by reference.

FIELD OF THE INVENTION

An embodiment of the invention is directed to a method for treatingpatients experiencing sacroiliac joint pain. More particularly, theinvention relates to a system for preparing a space between the sacrumand the iliac to facilitate sacroiliac joint fusion.

BACKGROUND OF THE INVENTION

The sacroiliac joint is located at the intersection of the ilium, theupper bone of the pelvis, and the sacrum at the base of the spine. Oneof the primary functions of the sacroiliac joint is to provide shockabsorption of pressures put on the spine.

Certain persons experience pain in the sacroiliac joint. This pain mayresult from a variety of causes, examples of which include injuries,incorrect vertebra fusion during pre-birth development and effects ofpregnancy.

If initial efforts to reduce the pain in the sacroiliac joint throughphysical therapy and/or steroid injections are not effective, surgerymay be needed to fuse together the sacroiliac joint. One typicalsurgical technique involves forming an incision in the lower back overthe sacroiliac joint. The articular cartilage is removed from bothsurfaces. This process is also called chondrectomy.

The sacrum and the ilium are held together with screws or a plate.Eventually, bone grows between the sacrum and the ilium to thereby fusetogether the sacroiliac joint. Because of the challenges in accessingthe surfaces of the sacrum and the ilium that will fuse together, thistype of surgery may result in damage to tissue, nerves and/or bloodvessels that surround the sacroiliac joint. Such damage may prevent thepatient from fully realizing the benefits of the sacroiliac joint fusionand in some instances cause the patient to experience more pain afterthe sacroiliac joint fusion than before the sacroiliac joint fusion.

SUMMARY OF THE INVENTION

An embodiment of the invention is directed to a method of performing anorthopedic procedure in the sacroiliac region. At least one aperture isformed that at least partially extends through at least one of an iliumand a sacrum. An undercutting system is inserted at least partially intothe aperture. The undercutting system includes an insertion apparatus, aprobe assembly and a cutting assembly.

The probe assembly is moved with respect to the insertion apparatus froma retracted position to an extended position. When in the retractedposition, the probe assembly is substantially within the insertionapparatus. When in the extended position, at least a portion of theprobe assembly extends from the insertion apparatus. The probe assemblyis manipulated within a joint between the ilium and the sacrum while theprobe assembly is in the extended position.

The cutting assembly is moved with respect to the insertion apparatusfrom a retracted position to an extended position. When in the retractedposition, the cutting assembly is substantially within the insertionapparatus. When in the extended position, at least a portion of thecutting assembly extends from the insertion apparatus. The cuttingassembly is sharper than the probe assembly. The cutting assembly ismanipulated within the joint between the ilium and the sacrum while thecutting assembly is in the extended position to form a fusion region.The undercutting system is removed from the aperture.

Another embodiment of the invention is directed to a method ofperforming an orthopedic procedure in the sacroiliac region. At leastone aperture is formed that at least partially extends through at leastone of an ilium and a sacrum. An undercutting system is inserted atleast partially into the aperture. The undercutting system includes acutting assembly.

The cutting assembly is moved to an extended position between the iliumand the sacrum where a portion of the cutting assembly extends beyond anouter periphery of the undercutting system. A fusion region is formed bymoving the cutting assembly between the ilium and the sacrum. Thecutting assembly is moved to a retracted position where the cuttingassembly is substantially within the outer periphery of the undercuttingsystem.

The undercutting system is removed from the aperture. A fastening deviceis inserted into the ilium aperture and the sacrum aperture. Thefastening device retains the ilium and the sacrum in a stationaryposition with respect to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 is a perspective view of an undercutting system for use in asacroiliac fusion procedure.

FIG. 2 is an exploded perspective view of the undercutting system.

FIG. 3 is a top view of the undercutting system.

FIG. 4 is a bottom view of the undercutting system.

FIG. 5 is a sectional view of the undercutting system taken along a lineA-A in FIG. 3.

FIG. 6 is a perspective view of an end portion of a probe assembly foruse with the undercutting system.

FIG. 7 is a top view of the end portion of the probe assembly of FIG. 6.

FIG. 8 is a side view of the end portion of the probe assembly of FIG.6.

FIG. 9 is a side view of the probe assembly of FIGS. 6-8 extending froma distal end of the insertion apparatus.

FIG. 10 is a perspective view of an end portion of an alternative probeassembly for use with the undercutting system.

FIG. 11 is a top view of the end portion of the probe assembly of FIG.10.

FIG. 12 is a side view of the end portion of the probe assembly of FIG.10.

FIG. 13 is a top view of an end portion of another probe assembly foruse with the undercutting system.

FIG. 14 is a side view of the end portion of the probe assembly of FIG.13.

FIG. 15 is a perspective view of an undercutting system for use in asacroiliac fusion procedure.

FIG. 16 is a top view of the end portion of the probe assembly of FIG.15.

FIG. 17 is a side view of the end portion of the probe assembly of FIG.15.

FIG. 18 is a perspective view of an undercutting system for use in asacroiliac fusion procedure.

FIG. 19 is a top view of the end portion of the probe assembly of FIG.18.

FIG. 20 is a side view of the end portion of the probe assembly of FIG.18.

FIG. 21 is a side view of an alternative configuration of anundercutting system for use in a sacroiliac fusion procedure.

FIG. 22 is a sectional view of the undercutting system of FIG. 6 takenalong a line A-A in FIG. 21.

FIG. 23 is a second side view of the undercutting system of FIG. 21.

FIG. 24 is an interior portion of the undercutting system of FIG. 21.

FIG. 25 is a sectional view of the interior portion of the undercuttingsystem of FIG. 6 taken along a line B-B in FIG. 24.

FIG. 26 is a side view of a cutting assembly extending over the probeassembly.

FIG. 27 is a perspective view of the cutting assembly extending over theprobe assembly.

FIG. 28 is an end view of the cutting assembly extending over the probeassembly.

FIG. 29 is a perspective view of another configuration of the cuttingassembly extending over the probe assembly.

FIG. 30 is a partially cut away perspective view of an aperture beingdrilled in the sacrum and the ilium as an initial step in a sacroiliacfusion procedure.

FIG. 31 is a partially cut away perspective view of an undercuttingsystem being inserted into the aperture.

FIG. 32 is a partially cut away perspective view of the undercuttingsystem being used to form an undercut region between the sacrum and theilium.

FIG. 33 is a partially cut away perspective view of fasteners insertedinto the apertures.

FIG. 34 is an inlet fluoroscope view illustrating a desired trajectoryfor the two fasteners.

FIG. 35 is an outlet fluoroscope view illustrating a desired trajectoryfor the two fasteners.

FIG. 36 is a lateral fluoroscope view of the pelvic region after twofasteners have been inserted.

FIG. 37 is an inlet fluoroscope view of the pelvic region after twofasteners have been inserted.

FIG. 38 is an outlet fluoroscope view of the pelvic region after twofasteners have been inserted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention is directed to an undercutting system 10,such as is illustrated in FIGS. 1-5. The undercutting system 10 may beused for preparing surfaces of the ilium 14 and the sacrum 16 forsacroiliac joint fusion, which are illustrated in FIG. 31. Theundercutting system utilizes an aperture 20 formed in the ilium 14 toaccess a region 22 between the ilium 14 and the sacrum 16.

In certain embodiments, the aperture 20 may have a diameter of up toabout 50 millimeters. In other embodiments, the aperture 20 may have adiameter of between about 5 millimeters and 20 millimeters.

The undercutting system 10 thereby enables tissue such as cartilage tobe removed from the adjacent surfaces of the ilium 14 and the sacrum 16and for at least a portion of the adjacent surfaces of the ilium 14 andthe sacrum 16 to be removed or otherwise disturbed. This procedure maybe referred to as preparing bleeding bone surfaces on the ilium 14 andthe sacrum 16, which are more receptive to growing bone between them aspart of sacroiliac joint fusion.

Thereafter, the ilium 14 and the sacrum 16 may be held in a stationaryposition with respect to each other such as by using a screw that isextended through the aperture 20, as is discussed in more detail below.Maintaining the ilium 14 and the sacrum 16 in the stationary positionfacilitates bone growth between the ilium 14 and the sacrum 16 tothereby fuse the sacroiliac joint.

Performing the sacroiliac fusion using the undercutting system 10disclosed herein reduces the complexity of the sacroiliac fusion whencompared to prior techniques used for sacroiliac fusion. Additionally,sacroiliac fusion performed using the concepts describe herein has thepotential of fewer side effects because this process does not requirethe surgeon to work proximate the nerves and/or blood vessels, as isdone with prior sacroiliac fusion techniques.

Furthermore, the apparatus and technique disclosed herein do notformally expose the sacroiliac joint to reduce the potential ofinfection. The time associated with preparing the surfaces of the iliumand the sacrum is also reduced when compared to the prior more invasivetechniques used to prepare the sacroiliac joint for fusion.

In one embodiment, the undercutting system 10, may include an insertionapparatus 30 and a probe assembly 32 that extends from a distal end ofthe insertion apparatus 30, as illustrated in FIGS. 1-5.

The insertion apparatus 30 may include an elongated shaft 40 that isformed with a length that enables a proximal end thereof to bepositioned outside of the patient's body while a distal end thereof isutilized to the prepare the region between the ilium 14 and the sacrum16 for the sacroiliac fusion process. In certain embodiments, the lengthof the elongated shaft 40 is between about 15 centimeters and about 45centimeters.

The elongated shaft 40 may be formed with a relatively small outerdiameter to minimize a size of the aperture 20 that needs to be formedin the ilium 14. The larger the aperture 20 that is formed in the ilium14, the greater the potential of the ilium 14 weakening to the point atwhich the ilium 14 is more susceptible to breakage. In certainembodiments, the outer diameter of the elongated shaft 40 is betweenabout 6 millimeters and 20 millimeters.

The insertion apparatus 30 may also include a handle portion 42proximate a proximal end thereof. The handle portion 42 enhances theability to manipulate the insertion apparatus 30 such as insertion,rotation and withdrawal.

The handle portion 42 may have a diameter that is greater than adiameter of the elongated shaft 40. In certain embodiments, the handleportion 42 has a diameter of between about 2 centimeters and about 20centimeters.

An outer edge of the handle portion 42 may have a plurality of concaveregions 44 formed therein. The concave regions 44 enhance the ability togrip the handle portion 42 and thereby manipulate the insertionapparatus 30.

The insertion apparatus 30 may further include a control knob 46 that isused for extending and retracting the probe assembly 32. In oneconfiguration of the insertion apparatus 30, the control knob 46 isrotatably mounted with respect to the insertion apparatus 30.

The control knob 46 may have a diameter that is different than adiameter of the handle portion 42. Forming the control knob 46 with adiameter that is different than a diameter of the handle portion 42minimizes the potential that a person using the insertion apparatus 30would inadvertently manipulate the insertion apparatus 30 or the controlknob 46.

The control knob 46 may have a diameter that is less than a diameter ofthe handle portion 42. In certain embodiments, the control knob 46 has adiameter of between about 2 centimeters and about 20 centimeters.

An outer edge of the control knob 46 may have a plurality of concaveregions 48 formed therein. The concave regions 48 enhance the ability togrip the control knob 46 and thereby manipulate the insertion apparatus30.

Rotation of the control knob 46 in a first direction causes the probeassembly 32 to be extended from the distal end of the insertionapparatus 30. Rotation of the control knob 46 in a second direction,which is opposite the first direction, causes the probe assembly 32 tobe retracted into the distal end of the insertion apparatus 30.

The insertion apparatus 30 may also include a lock screw 50 operablyattached hereto. The lock screw 50 may be oriented generally transverseto the elongated shaft 40 and may be positioned proximate the handleportion 42. The lock screw 50 may threadably engage the elongated shaft40.

The lock screw 50 may be positioned in an engaged position where adistal end of the lock screw 50 extends into the interior of theelongated shaft 40 until the distal end engages a shaft that extendsbetween the probe assembly 32 and the control knob 46. The lock screw 50thereby retains the shaft in a fixed position with respect to theelongated shaft 40 to prevent movement of the probe assembly 32 withrespect to the insertion apparatus 30.

Rotating the lock screw 50 in an opposite direction causes the distalend to not engage the cutter shaft so that the shaft may be moved withrespect to the elongated shaft 40 to move the probe assembly 32 betweenthe extended and retracted positions.

Inside at least a portion of the elongated shaft 40 is a controlmechanism 60 that operably attaches the probe assembly 32 to the otherportions of the insertion apparatus 30, as most clearly illustrated inFIGS. 2 and 5. A primary function of the control mechanism 60 is tofacilitate extension and retraction of the probe assembly 32.

When the probe assembly 32 is in the retracted position, the probeassembly 32 is within an outer periphery of the insertion apparatus 30.Using such a configuration enables the elongated shaft 40 to be insertedinto the patient using a cannula having an inner diameter that isapproximately the same as an outer diameter of the elongated shaft 40.

The control mechanism 60 may generally include a first attachmentsection 62 and a second attachment section 64. The first attachmentsection 62 is attached to the control knob 46. In one configuration, thefirst attachment section 62 is fixedly attached to the control knob 46so that the first section 62 rotates when the control knob 46 isrotated.

The first attachment section 62 may have a length that is less than thelength of the elongated shaft 40. In certain embodiments, the firstattachment section 62 has a length that is approximately one-half of thelength of the elongated shaft 40.

The first attachment section 62 may have a generally cylindrical shapewith an outer diameter that is slightly smaller than an inner diameterof the elongated shaft 40, as most clearly illustrated in FIG. 5.Forming the first attachment section 62 with this shape facilitatesrotating and sliding of the first attachment section 62 with respect tothe elongated shaft 40.

A distal end of the first attachment section 62 has a connectionmechanism 66 that facilitates attaching the second attachment section 64to the first attachment section 62. In one such configuration, theconnection mechanism 66 includes a recess 70 formed in the distal end.The recess 70 may have a width and a depth that is greater that a widthand a depth of the proximal end of the second attachment section 64.

An attachment pin 72 may be provided in the recess 70 that enables thesecond attachment section 64 to engage the connection mechanism 66. Incertain embodiments, the attachment pin 72 may be oriented generallyperpendicular to the first attachment section 62.

An aperture 74 may be formed in the proximal end of the secondattachment section 64. The aperture 74 may have a diameter that isslightly larger than a diameter of the attachment pin 72. Using such aconfiguration, the attachment pin 72 may extend into the aperture 74 toretain the first attachment section 62 in a fixed relationship withrespect to the second attachment section 64.

Forming the connection mechanism 66 with preceding configuration allowsthe second attachment section 64 to be attached to the first attachmentsection 62 when the first attachment section 62 and the secondattachment section 64 are not covered by the elongated shaft 40.

On the other hand, when the elongated shaft 40 is placed over firstattachment section 62 and the second attachment section 64, the secondattachment section 64 is retained in engagement with the firstattachment section 62.

A person of skill in the art will appreciate that it is possible toattach the first attachment section 62 and the second attachment section64 using different structures, which enable sliding and rotating of thefirst attachment section 62 and the second attachment section 64 withrespect to the elongated shaft 40.

While the figures illustrate that a mechanical connection is providedbetween the probe assembly 32 and the other components of theundercutting system 10, it is also possible to utilize an electricalconnection between the probe assembly 32 and the other components of theundercutting system 10. Such an electrical connection may utilizeswitches and actuators. It is also possible to use pneumatic andhydraulic systems to operably connect the probe assembly 32 and theother components of the undercutting system 10.

The mechanical connection between the probe assembly 32 and the othercomponents of the undercutting system 10 provides a mechanical advantagethat enables the probe assembly 32 to be extended from the insertionapparatus much more easily and controllably than if the undercuttingsystem did not include the mechanical connection.

The invention thereby minimizes the potential of the probe assembly 32being damaged during the insertion process. This invention also enhancesthe control over the size of the fusion region that is prepared.

The connection mechanism 66 may also include a ball-type connector 80that attaches the connection mechanism 66 to the first attachmentsection 62. The ball-type connector 80 may include a ball-shapedextension 82 on the connection mechanism 66 and a recess 84 formed inthe distal end of the first attachment section 62. The recess 84 has ashape that is generally complementary to the shape of the ball-shapedextension 82.

Similar to the attachment between the connection mechanism 66 and thesecond attachment section 64, the ball-type connector 80 allows thefirst attachment section 62 to be attached to the connection mechanism66 when the first attachment section 62 and the connection mechanism 66are not covered by the elongated shaft 40.

On the other hand, when the elongated shaft 40 is placed over firstattachment section 62 and the connection mechanism 66, the ball-shapedextension 82 is retained in engagement with the recess 84.

The probe assembly 32 is attached to the distal end of the secondattachment section 64. To accommodate using probe assemblies 32 havingdifferent lengths, the undercutting system 10 may be provided with morethan one second attachment section 64 having different lengths.Alternatively or additionally, the undercutting system 10 may includemore than one first attachment section 62 having different lengths.Using such a configuration enables one of the first attachment sections62 and the second attachment sections 64 to be selected based upon thelength of the probe assembly 32.

A benefit of using the ball-shaped extension 82 is that this connectionmechanism enables the control handle to rotate such as when extending orretracting the probe assembly 32 with respect to the insertion apparatus30 without having the probe assembly 32 rotate.

The distal end of the second attachment section 64 may have a recess 90formed therein. The recess 90 may have a depth that is greater than athickness of the proximal end of the probe assembly 32. The recess 90may extend across at least a portion of a width of the second attachmentsection 64.

An attachment pin 92 may be provided in the recess 90 that enables theprobe assembly 32 to engage the second attachment section 64. In certainembodiments, the attachment pin 92 may be oriented generallyperpendicular to the second attachment section 64.

The second attachment section 64 may be formed with a height and a widththat are both slightly smaller than a height and a width of a channel 96that is formed in an end cap 100, which is discussed in more detailbelow. Forming the second attachment section 64 with these dimensionsenables the second attachment section 64 to slide in the channel 96.

The cap 100 may be positioned in the distal end of the elongated shaft40, as most clearly illustrated in FIG. 5. The cap 100 thereby seals theelongated shaft 40 to generally restrict tissue and fluid from enteringthe elongated shaft 40.

While it is possible for a distal end of the cap 100 to be orientedgenerally transverse to the elongated shaft 40, the distal end of thecap 100 may be oriented at an angle of less than about 90 degrees withrespect to the elongated shaft 40. In certain embodiments, the distalend of the cap 100 is oriented at an angle of between about 45 degreesand about 60 degrees, as illustrated in FIG. 5.

As referenced above, the cap 100 has the channel 96 formed therein.Proximate the proximal end, the channel 96 may be generally aligned withbut offset from a central axis of the elongated shaft 40. Proximate thedistal end, the channel 96 may be oriented generally perpendicular tothe central axis of the elongated shaft 40. The channel 96 therebyenables the probe assembly 32 to emerge from the insertion apparatus ina direction that is generally aligned with the surface of at least oneof the ilium 14 and the sacrum 16.

Intermediate the proximal end and the distal end, the channel 96 iscurved. The radius of curvature may be determined by a variety offactors. An example of one such factor is the flexibility of the portionof the probe assembly 32.

The channel 96 thereby causes the probe assembly 32 to be deflected suchthat when the probe assembly 32 extends from the cap 100, the probeassembly 32 is oriented in a direction that is generally transverse tothe elongated shaft 40, as illustrated in FIG. 5, so that the probeassembly 32 can be extended into the region between the ilium 14 and thesacrum 16.

The cap 100 may have an aperture 106 that extends therethrough that isgenerally perpendicular to the axis of the elongated shaft 40. Theelongated shaft 40 may also include an aperture that is generallyaligned with the aperture 106 when the cap 100 is placed into the distalend of the elongated shaft 40. A pin 110 is extended through theaperture 106 and the aperture to thereby retain the cap 100 in astationary position with respect to the elongated shaft 40.

The probe assembly 32 may have a variety of configurations, as isdiscussed in more detail herein. In one such embodiment, the probeassembly 32 may have an elongated configuration, as illustrated in FIGS.2 and 6-8, where a proximal end 120 thereof is operably attached to thesecond attachment section 64 and a distal end 122 thereof extends fromthe undercutting system 10. This embodiment of the probe assembly 32 maybe particularly useful for initial use to locate a surface of the ilium14 and/or the sacrum 16.

The probe assembly 32 may have a thickness of up to about 2 millimeters.In certain embodiments, the probe assembly 32 may have a thickness ofbetween about 0.4 millimeters and about 0.6 millimeters. Using the probeassembly 32 with the preceding dimensions provides the probe assembly 32with flexibility in a distal-proximal direction while resisting twistingor otherwise deforming.

The resistance enables the probe assembly 32 to deflect in response tochanges in the shape or orientation of the ilium 14 or the sacrum 16.Such deflection is important because it is much more difficult to cutthrough the bone of the ilium 14 and the sacrum 16 than the cartilagethat is between the ilium 14 and the sacrum 16.

The configuration of the probe assembly 32 provides the probe assembly32 with sufficient rigidity in a radial direction. Such a configurationallows the probe assembly 32 to resist deformation in response torotation of the undercutting system 10 such as when the tissue betweenthe ilium 14 and the sacrum 16 is contacted with the probe assembly 32.

The probe assembly 32 may have a width that is no greater than an innerdiameter of the elongated shaft 40. Forming the probe assembly 32 withsuch a configuration enables the probe assembly 32 to be positionedsubstantially within a profile of the elongated shaft 40 when the probeassembly 32 is in a retracted configuration so that the probe assembly32 does not interfere with the insertion of the distal end of theundercutting system 10 through the aperture 20 in the ilium 14.

The probe assembly 32 may have a width of between about 2 millimetersand about 5 millimeters. In certain embodiments, the probe assembly 32may have a width of about 3 millimeters.

Side edges of the probe assembly 32 may be sufficient to cut through thetissue between the ilium 14 and the sacrum 16. Using the probe assembly32 without the sharpened edges may reduce a tendency of the probeassembly 32 to cut into the ilium 14 and the sacrum 16 while the probeassembly 32 is rotated.

This process thereby allows an initial path between the ilium 14 and thesacrum 16 to be defined. This process is identified as defining a jointline. As is discussed in more detail below, the adjacent surfaces of theilium 14 and the sacrum 16 may not be oriented substantially parallel toeach other or substantially transverse to the orientation of theaperture 20.

When defining the joint line, the probe assembly 32 passes through theintra-articular region between the ilium 14 and the sacrum 16. Thecartilage and ligaments in the intra-articular region are considerablyeasier to cut than the ilium 14 and the sacrum 16.

Once this path is defined, it is possible to use a cutting assembly suchas is described herein to prepare a wider region between the ilium 14and the sacrum 16 as part of the sacroiliac fusion process.

By using this process, the potential of the cutting assembly cutting toodeeply into the ilium 14 or the sacrum 16 is reduced because the cuttingassembly will follow the joint line that was defined by the probeassembly 32.

Alternatively, the probe assembly 32 may include a cutting surface on atleast one edge thereof. In certain embodiments, cutting surfaces areprovided on both side edges of the probe assembly 32. Providing thecutting surfaces on the side edges enhances the ability of the probeassembly 32 to cut while being rotated in clockwise and counterclockwise directions.

In certain embodiments, a distal end of the probe assembly 32 may nothave a cutting surface. Forming the distal end without the cuttingsurface reduces a tendency of the probe assembly 32 to cut into theilium 14 or the sacrum 16 as the probe assembly 32 is extended from theinsertion apparatus 30.

An aperture 94 may be formed in the proximal end of the probe assembly32. The aperture 94 may have a diameter that is slightly larger than adiameter of the attachment pin 92. Using such a configuration, theattachment pin 92 may extend into the aperture 94 to retain the probeassembly 32 in a fixed relationship with respect to the secondattachment section 64.

The aperture 94 should not be too large such that the aperture 94weakens the cutting assembly 32, which could cause the probe assembly 32to fail when a force is applied to the probe assembly 32 such as occursduring the use of the undercutting system to cut tissue from between theilium 14 and the sacrum 16.

The aperture 94 may be generally circular and may have a diameter ofbetween about 0.5 millimeters and about 5 millimeters. In otherembodiments, the aperture 94 may have a diameter of between about 1.5millimeters and about 2 millimeters.

A person of skill in the art will appreciate that it is possible toattach the second attachment section 64 and the probe assembly 32 usingdifferent structures, which enable sliding and rotating of the secondattachment section 64 and the probe assembly 32 with respect to theelongated shaft 40.

The probe assembly 32 having the preceding shape and characteristics maybe formed from a variety of materials. A person of skill in the art willappreciate that the material used to fabricate the probe assembly 32should be suitable for use within a human body. An example of one suchmaterial for fabricating the probe assembly 32 is nitinol. A beneficialquality of nitinol is that nitinol is bendable but returns to the unbentconfiguration when the force that caused the bending is removed.

The probe assembly 32 is extended from the distal end of the insertionapparatus 30, as illustrated in FIG. 9. The insertion apparatus 30 isthen rotated to cause the probe assembly 32 to be move through thetissue between the ilium 14 and the sacrum 16. Rotation of the insertionapparatus 30 may be in a single direction or may alternatively be inclockwise and counterclockwise directions. This rotation may becontinued until minimal resistance is felt during the rotation of theinsertion apparatus 30.

In another embodiment, a cutting element 234 may be attached proximate adistal end of the probe assembly 32, which is illustrated in FIGS. 6-8,to form a cutting assembly 232, as illustrated in FIGS. 10-12.

The cutting assembly 232 may have a thickness of up to about 2millimeters. In certain embodiments, the cutting assembly 232 may have athickness of between about 0.4 millimeters and about 0.6 millimeters.Using the cutting assembly 232 with the preceding dimensions providesthe cutting assembly 232 with flexibility in a distal-proximal directionwhile resisting twisting or otherwise deforming.

The resistance enables the cutting assembly 232 to deflect in responseto changes in the shape or orientation of the ilium 14 or the sacrum 16.Such deflection is important because it is much more difficult to cutthrough the bone of the ilium 14 and the sacrum 16 than the cartilagethat is between the ilium 14 and the sacrum 16.

The configuration of the cutting assembly 232 provides the cuttingassembly 232 with sufficient rigidity in a radial direction. Such aconfiguration allows the cutting assembly 232 to resist deformation inresponse to rotation of the undercutting system 10 during the cuttingprocess such as when the tissue between the ilium 14 and the sacrum 16is contacted with the cutting assembly 232.

The cutting assembly 232 may have a width that is no greater than aninner diameter of the elongated shaft 40. Forming the cutting assembly232 with such a configuration enables the cutting assembly 232 to bepositioned substantially within a profile of the elongated shaft 40 whenthe cutting assembly 232 is in a retracted configuration so that thecutting assembly 232 does not interfere with the insertion of the distalend of the undercutting system 10 extending through the aperture 20 inthe ilium 14.

The cutting assembly 232 may have a width of between about 2 millimetersand about 5 millimeters. In certain embodiments, the cutting assembly232 may have a width of about 3 millimeters.

Side edges of the cutting assembly 232 may be sufficient to cut throughthe tissue between the ilium 14 and the sacrum 16. Using the cuttingassembly 232 without the sharpened edges may reduce a tendency of thecutting assembly 232 to cut into the ilium 14 and the sacrum 16 whilethe cutting assembly 232 is rotated.

Alternatively, the cutting assembly 232 may include a cutting surface onat least one edge thereof. In certain embodiments, cutting surfaces areprovided on both side edges of the cutting assembly 232. Providing thecutting surfaces on the side edges enhances the ability of the cuttingassembly 232 to cut while being rotated in clockwise and counterclockwise directions.

In certain embodiments, a distal end of the cutting assembly 232 may nothave a cutting surface. Forming the distal end without the cuttingsurface reduces a tendency of the cutting assembly 232 to cut into theilium 14 or the sacrum 16 as the cutting assembly 232 is advanced fromthe insertion apparatus 30.

An aperture 294 may be formed in the proximal end of the cuttingassembly 232. The aperture 294 may have a diameter that is slightlylarger than a diameter of the attachment pin 92. Using such aconfiguration, the attachment pin 92 may extend into the aperture 294 toretain the cutting assembly 232 in a fixed relationship with respect tothe second attachment section 64.

The aperture 294 should not be too large such that the aperture 294weakens the cutting assembly 232, which could cause the cutting assembly232 to fail when a force is applied to the cutting assembly 232 such asoccurs during the use of the undercutting system to cut tissue frombetween the ilium 14 and the sacrum 16.

The aperture 294 may be generally circular and may have a diameter ofbetween about 0.5 millimeters and about 5 millimeters. In otherembodiments, the aperture 294 may have a diameter of between about 1.5millimeters and about 2 millimeters.

A person of skill in the art will appreciate that it is possible toattach the second attachment section 64 and the cutting assembly 232using different structures, which enable sliding and rotating of thesecond attachment section 64 and the cutting assembly 232 with respectto the elongated shaft 40.

The cutting assembly 232 having the preceding shape and characteristicsmay be formed from a variety of materials. A person of skill in the artwill appreciate that the material used to fabricate the cutting assembly232 should be suitable for use within a human body. An example of onesuch material for fabricating the cutting assembly 232 is nitinol. Abeneficial quality of nitinol is that nitinol is bendable but returns tothe unbent configuration when the force that caused the bending isremoved.

In certain embodiments, the cutting element 234 may have a generallycylindrical configuration that extends from at least one side of thecutting assembly 232. The cutting element 234 may extend insubstantially equal distances on opposite sides of the cutting assembly232.

A distance between the distal surfaces of the cutting element 234 may belimited by the inner diameter of the elongated shaft 40 so that thecutting assembly 232 with the cutting element 234 attached thereto maybe retracted within the insertion apparatus 30 when the insertionapparatus 30 is inserted into and removed from the region between theilium 14 and the sacrum 16.

In certain embodiments, a height of the cutting element 234 on oppositesides of the cutting assembly 232 is between about 1 millimeter andabout 5 millimeters. In other embodiments, the height of the cuttingelement 234 on opposite sides of the cutting assembly 232 is about 2millimeters.

While it is illustrated that the height of the cutting element 234 isapproximately equal on opposite sides of the cutting assembly 232, it ispossible to configure the cutting element so that the height of thecutting element 234 on opposite sides of the cutting assembly 232 is notapproximately equal.

In certain embodiments, a diameter of the cutting element 234 may bebetween about 1 millimeter and about 5 millimeters. In otherembodiments, the diameter of the cutting element 234 may be about 3millimeters.

While it is illustrated that the diameter of the cutting element 234 isapproximately equal on opposite sides of the cutting assembly 232, it ispossible to configure the cutting element so that the diameter of thecutting element 234 on opposite sides of the cutting assembly 232 is notapproximately equal.

An edge 136 of the cutting element 234 proximate the distal ends thereofmay be sufficient to cut through the tissue between the ilium 14 and thesacrum 16. Using the cutting element 234 without the sharpened edges mayreduce a tendency of the cutting element 234 to cut into the ilium 14and the sacrum 16 while the cutting assembly 232 is rotated. In otherembodiments, the cutting element 234 may have a diameter proximate thecutting assembly 232 that is less than a diameter distal the cuttingassembly 232.

Alternatively, the edge 236 of the cutting element 234 proximate thedistal ends thereof may be sharpened to facilitate cutting of tissueproximate the surfaces of the ilium 14 and the sacrum 16.

A distance between the distal ends of the cutting element 234 therebydefines a thickness of a region between the ilium 14 and the sacrum 16that is prepared with the undercutting system 10.

The undercutting system 10 may include a plurality of cutting assemblies232 having cutting elements 234 with different distances between thedistal ends thereof. One of the cutting assemblies 232 having thecutting element 234 with the smallest distance between the distal endsmay be initially used. Thereafter, cutting assemblies 232 having thecutting elements 234 with progressively longer distances between thedistal ends may be used to form a progressively wider region between theilium 14 and the sacrum 16.

While it is desirable to prepare the surfaces of the ilium 14 and thesacrum 16 by exposing bleeding bone, it is desirable to avoid thecutting assembly 232 and the cutting element 234 digging into thesurface of the ilium 14 or the sacrum 16 too deeply. When the cuttingassembly 232 digs too deeply into the surface of the ilium 14 or thesacrum 16, it becomes more difficult to rotate the cutting assembly 232because the ilium 14 and the sacrum 16 are much harder than the tissuelocated between the ilium 14 and the sacrum 16. The cutting assembly 232and the cutting element 234 having the characteristics set forth abovemeet these criteria.

The cutting element 234 having the preceding shape and characteristicsmay be formed from a variety of materials. A person of skill in the artwill appreciate that the material used to fabricate the cutting element234 should be suitable for use within a human body. An example of onesuch suitable material for fabricating the cutting element 234 isstainless steel.

The cutting element 234 may be attached to the cutting assembly 232using a variety of techniques that cause the cutting element 234 to befixedly attached to the cutting assembly 232. One such suitabletechnique for attaching the cutting element 234 to the cutting assembly232 is welding.

Alternatively, it is possible to fabricate the cutting assembly 232 andthe cutting element 234 as a single unit such as by machining a block toprovide the substantially flat cutting assembly 232 and the cuttingelement 234 that extends from the cutting assembly 232.

In another embodiment, a cutting element 334 may be attached proximate adistal end of the probe assembly 32, which is illustrated in FIGS. 6-8,to form a cutting assembly 332, as illustrated in FIGS. 13 and 14.

The cutting assembly 332 may have a thickness of up to about 2millimeters. In certain embodiments, the cutting assembly 332 may have athickness of between about 0.4 millimeters and about 0.6 millimeters.Using the cutting assembly 332 with the preceding dimensions providesthe cutting assembly 332 with flexibility in a distal-proximal directionwhile resisting twisting or otherwise deforming.

The resistance enables the cutting assembly 332 to deflect in responseto changes in the shape or orientation of the ilium 14 or the sacrum 16.Such deflection is important because it is much more difficult to cutthrough the bone of the ilium 14 and the sacrum 16 than the tissue thatis between the ilium 14 and the sacrum 16.

The configuration of the cutting assembly 332 provides the cuttingassembly 332 with sufficient rigidity in a radial direction. Such aconfiguration allows the cutting assembly 332 to resist deformation inresponse to rotation of the undercutting system 10 during the cuttingprocess such as when the tissue between the ilium 14 and the sacrum 16is contacted with the cutting assembly 332.

The cutting assembly 332 may have a width that is no greater than aninner diameter of the elongated shaft 40. Forming the cutting assembly332 with such a configuration enables the cutting assembly 332 to bepositioned substantially within a profile of the elongated shaft 40 whenthe cutting assembly 332 is in a retracted configuration so that thecutting assembly 332 does not interfere with the insertion of the distalend of the undercutting system 10 extending through the aperture 20 inthe ilium 14.

The cutting assembly 332 may have a width of between about 2 millimetersand about 5 millimeters. In certain embodiments, the cutting assembly332 may have a width of about 3 millimeters.

Side edges of the cutting assembly 332 may be sufficient to cut throughthe tissue between the ilium 14 and the sacrum 16. Using the cuttingassembly 332 without the sharpened edges may reduce a tendency of thecutting assembly 332 to cut into the ilium 14 and the sacrum 16 whilethe cutting assembly 332 is rotated to cut the tissue that is betweenthe ilium 14 and the sacrum 16.

Alternatively, the cutting assembly 332 may include a cutting surface onat least one edge thereof. In certain embodiments, cutting surfaces areprovided on both side edges of the cutting assembly 332. Providing thecutting surfaces on the side edges enhances the ability of the cuttingassembly 332 to cut while being rotated in clockwise and counterclockwise directions.

In certain embodiments, a distal end of the cutting assembly 332 may nothave a cutting surface. Forming the distal end without the cuttingsurface reduces a tendency of the cutting assembly 332 to cut into theilium 14 or the sacrum 16 as the cutting assembly 332 is advanced fromthe insertion apparatus 30.

An aperture 394 may be formed in the proximal end of the cuttingassembly 332. The aperture 394 may have a diameter that is slightlylarger than a diameter of the attachment pin 92. Using such aconfiguration, the attachment pin 92 may extend into the aperture 394 toretain the cutting assembly 332 in a fixed relationship with respect tothe second attachment section 64.

The aperture 394 should not be too large such that the aperture 394weakens the cutting assembly 332, which could cause the cutting assembly332 to fail when a force is applied to the cutting assembly 332 such asoccurs during the use of the undercutting system to cut tissue frombetween the ilium 14 and the sacrum 16.

The aperture 394 may be generally circular and may have a diameter ofbetween about 0.5 millimeters and about 5 millimeters. In otherembodiments, the aperture 394 may have a diameter of between about 1.5millimeters and about 2 millimeters.

A person of skill in the art will appreciate that it is possible toattach the second attachment section 64 and the cutting assembly 332using different structures, which enable sliding and rotating of thesecond attachment section 64 and the cutting assembly 332 with respectto the elongated shaft 40.

The cutting assembly 332 having the preceding shape and characteristicsmay be formed from a variety of materials. A person of skill in the artwill appreciate that the material used to fabricate the cutting assembly332 should be suitable for use within a human body. An example of onesuch material for fabricating the cutting assembly 332 is nitinol. Abeneficial quality of nitinol is that nitinol is bendable but returns tothe unbent configuration when the force that caused the bending isremoved.

In certain embodiments, the cutting element 334 may have a generallyplanar configuration that extends from at least one side of the cuttingassembly 332. The cutting element 334 may extend in substantially equaldistances on opposite sides of the cutting assembly 332. The cuttingelement 334 may have a generally rectangular shape that is defined by adistal edge 340 and a pair of side edges 342.

While it is illustrated that a height of the cutting element 334 isapproximately equal on opposite sides of the cutting assembly 332, it ispossible to configure the cutting element 334 so that the height of thecutting element 334 is not approximately equal on opposite sides of thecutting assembly 332.

The height of the distal edge 340 may be limited by the inner diameterof the elongated shaft 40 so that the cutting assembly 332 may beretracted within the insertion apparatus 30 when the insertion apparatus30 is inserted into and removed from the region between the ilium 14 andthe sacrum 16.

In certain embodiments, the height of the cutting element 334 onopposite sides of the cutting assembly 332 is between about 1 millimeterand about 5 millimeters. In other embodiments, the height of the cuttingelement 334 on opposite sides of the cutting assembly 332 is about 3millimeters.

In certain embodiments, a width of the cutting element 334 isapproximately the same on opposite sides of the cutting assembly 332.The width of the cutting element 334 may be between about 1 millimeterand about 5 millimeters. In other embodiments, the width of the cuttingelement 334 is about 3 millimeters.

Corners proximate the intersection of the distal edge 340 and each ofthe side edges 342 may be curved. While such curvature could reduce thecutting ability of the cutting element 334 that could be attained if thedistal edge 340 and the side edge 342 intersected at a corner, thiscurvature may reduce the tendency of the cutting element 334 to dig toodeeply into the surfaces of the ilium 14 and the sacrum 16. As a resultof this configuration, the cutting element 334 would preferentially cutinto the tissue between the ilium 14 and the sacrum 16 as opposed tocutting the ilium 14 and the sacrum 16.

While it is illustrated that the cutting element 334 has a substantiallyequal thickness, it is possible for the thickness of the cutting element334 to vary. In certain embodiments, the thickness of the cuttingelement 334 may be greater proximate to the cutting assembly 332 toresist bending or deformation of the cutting element 334.

In certain embodiments, a thickness of the cutting element 334 may bebetween about 0.2 millimeters and about 2 millimeters. In otherembodiments, the thickness of the cutting element 334 may be about 0.5millimeters.

While it is illustrated that the thickness of the cutting element 334 isapproximately equal on opposite sides of the cutting assembly 332, it ispossible to configure the cutting element 334 so that the thickness ofthe cutting element 334 on opposite sides of the cutting assembly 332 isnot approximately equal.

The edge 340 of the cutting element 334 proximate the distal endsthereof may be sufficient to cut through the tissue between the ilium 14and the sacrum 16. Using the cutting element 334 without the sharpenededges may reduce a tendency of the cutting element 334 to cut into theilium 14 and the sacrum 16 while the cutting assembly 332 is rotated.

Alternatively, the edge 236 of the cutting element 334 proximate thedistal ends thereof may be sharpened to facilitate cutting of tissueproximate the surfaces of the ilium 14 and the sacrum 16.

The cutting element 334 may be oriented at an angle with respect to thecutting assembly 332 so that the cutting element 334 is not generallyparallel to the length of the cutting assembly 332. In certainembodiments, the cutting element 334 may be oriented at an angle ofbetween about 0 degrees and about 60 degrees. In other embodiments, theangle between the cutting element 334 and the cutting assembly 332 maybe about 30 degrees.

Orienting the cutting element 334 at the angle with respect to thelength of the cutting assembly 332 causes one of the edges to bedisposed forwardly. Such a configuration may increase the ability of thecutting element 334 to cut tissue from between the ilium 14 and thesacrum 16 as the cutting element 334 is rotated.

While it is illustrated that the cutting element 334 is orientedgenerally transverse to the surface of the cutting assembly 332, it ispossible for the cutting element 334 to be oriented at an angle withrespect to the surface of the cutting assembly 332. In certainembodiments, the angle between the cutting element 334 and the surfaceof the cutting assembly 332 may be between about 60 degrees and about 90degrees.

While it is possible for the cutting element 334 to be placed at thedistal end of the cutting assembly 332, in certain embodiments, thecutting element 334 is mounted a distance from the distal end of thecutting assembly 332. Mounting the cutting element 334 a distance fromthe distal end of the cutting assembly 332 enables the cutting assembly332 to define a path through the tissue between the ilium 14 and thesacrum 16, as opposed to the cutting element 334 being the primarycomponent that defines the path through the tissue between the ilium 14and the sacrum 16.

A distance between the cutting element 334 and the distal end of thecutting assembly 332 may be between about 1 millimeter and about 5millimeters. In other embodiments, the distance between the cuttingelement 334 and the distal end of the cutting assembly 332 may be about3 millimeters.

The cutting element 334 may be positioned at a location that isapproximately intermediate between the side edges of the cuttingassembly 332. Placing the cutting element 334 in this location mayreduce twisting of the cutting assembly 332, which could potentiallyoccur if the cutting element 334 was located closer to one of the sideedges of the cutting assembly 332.

The cutting element 334 having the preceding shape and characteristicsmay be formed from a variety of materials. A person of skill in the artwill appreciate that the material used to fabricate the cutting element334 should be suitable for use within a human body. An example of onesuch material for fabricating the cutting element 334 is nitinol.

In certain embodiments, the cutting assembly 332 may be fabricatedseparately from the cutting element 334. Forming the structure in thismanner enables different materials to be used for fabricating thecutting assembly 332 and the cutting element 334 so that the respectivematerials may be optimized based upon the function of the associatedstructure.

The cutting element 334 may be attached to the cutting assembly 332using a variety of techniques that cause the cutting element 334 to befixedly attached to the cutting assembly 332. One such suitabletechnique for attaching the cutting element 334 to the cutting assembly332 is welding.

Alternatively, it is possible to fabricate the cutting assembly 332 andthe cutting element 334 as a single unit such as by machining a block toprovide a substantially flat cutting assembly 332 and a cutting element334 that extends from the cutting assembly 332.

The undercutting system 10 may include a plurality of cutting assemblies332 with cutting elements 334 having different distances between thedistal ends thereof. One of the cutting assemblies 332 with the cuttingelement 334 having the smallest distance between the distal ends thereofmay be initially used. Thereafter, cutting assemblies 332 with cuttingelement 334 having progressively longer distances between the distalends thereof may be used to form a progressively wider region betweenthe ilium and the sacrum.

Placing the cutting element 334 on the relatively flexible cuttingassembly 332 enables the region between the ilium 14 and the sacrum 16to be prepared for the sacroiliac fusion while minimizing the cuttingassembly 332 digging into the surface of the ilium 14 or the sacrum 16.

While it is desirable to prepare the surfaces of the ilium 14 and thesacrum 16 by exposing bleeding bone, it is desirable to avoid thecutting assembly 332 digging into the surface of the ilium 14 or thesacrum 16 too deeply. When the cutting assembly 332 digs too deeply intothe surface of the ilium 14 or the sacrum 16, it becomes more difficultto rotate the cutting assembly 332 because the ilium 14 and the sacrum16 are much harder than the tissue located between the ilium 14 and thesacrum 16. The cutting assembly 332 and the cutting element 334 havingthe characteristics set forth above meet these criteria.

In another embodiment, the cutting assembly 432 may have an initialelongated shape that is generally similar to the shape of the probeassembly 32 illustrated in FIGS. 6-8. However, the cutting assembly 432may include two cutting assembly strips 432 a, 432 b that each have aplurality of waves 440 formed therein, as illustrated in FIGS. 15-17.

The cutting assembly strips 432 a, 432 b may have a thickness of up toabout 2 millimeters. In certain embodiments, the cutting assembly strips432 a, 432 b may have a thickness of between about 0.1 millimeters andabout 0.3 millimeters. Using the cutting assembly strips 432 a, 432 bwith the preceding dimensions provides the cutting assembly strips 432a, 432 b with flexibility in a distal-proximal direction while resistingtwisting or otherwise deforming.

The resistance enables the cutting assembly strips 432 a, 432 b todeflect in response to changes in the shape or orientation of the ilium14 or the sacrum 16. Such deflection is important because it is muchmore difficult to cut through the bone of the ilium 14 and the sacrum 16than the tissue that is between the ilium 14 and the sacrum 16.

The configuration of the cutting assembly strips 432 a, 432 b providesthe cutting assembly strips 432 a, 432 b with sufficient rigidity in aradial direction. Such a configuration allows the cutting assemblystrips 432 a, 432 b to resist deformation in response to rotation of theundercutting system during the cutting process such as when the tissuebetween the ilium 14 and the sacrum 16 is contacted with the cuttingassembly 432.

The cutting assembly strips 432 a, 432 b may have a width that is nogreater than an inner diameter of the elongated shaft 40. Forming thecutting assembly strips 432 a, 432 b with such a configuration enablesthe cutting assembly 432 to be positioned substantially within a profileof the elongated shaft 40 when the cutting assembly 432 is in aretracted configuration so that the cutting assembly 432 does notinterfere with the insertion of the distal end of the undercuttingsystem extending through the aperture 20 in the ilium 14.

The cutting assembly strips 432 a, 432 b may have a width of betweenabout 2 millimeters and about 5 millimeters. In certain embodiments, thecutting assembly strips 432 a, 432 b may have a width of about 3millimeters.

Side edges of the cutting assembly strips 432 a, 432 b may be sufficientto cut through the tissue between the ilium 14 and the sacrum 16. Usingthe cutting assembly strips 432 a, 432 b without the sharpened edges mayreduce a tendency of the cutting assembly 432 to cut into the ilium 14and the sacrum 16 while the cutting assembly 432 is rotated.

Alternatively, the cutting assembly strips 432 a, 432 b may include acutting surface on at least one edge thereof. In certain embodiments,cutting surfaces are provided on both side edges of the cutting assemblystrips 432 a, 432 b. Providing the cutting surfaces on the side edgesenhances the ability of the cutting assembly 432 to cut the tissuebetween the ilium 14 and the sacrum 16 while the cutting assembly 432 isrotated in clockwise and counter clockwise directions.

In certain embodiments, a distal end of the cutting assembly strips 432a, 432 b may not have a cutting surface. Forming the distal end withoutthe cutting surface reduces a tendency of the cutting assembly 432 tocut into the ilium 14 or the sacrum 16 as the cutting assembly 432 isadvanced from the insertion apparatus 30.

An aperture 494 may be formed in the proximal end of the cuttingassembly 432. The aperture 494 may have a diameter that is slightlylarger than a diameter of the attachment pin 92. Using such aconfiguration, the attachment pin 92 may extend into the aperture 494 toretain the cutting assembly 432 in a fixed relationship with respect tothe second attachment section 64.

The aperture 494 should not be too large such that the aperture 494weakens the cutting assembly 432, which could cause the cutting assembly432 to fail when a force is applied to the cutting assembly 432 such asoccurs during the use of the undercutting system to cut tissue frombetween the ilium 14 and the sacrum 16.

The aperture 494 may be generally circular and may have a diameter ofbetween about 0.5 millimeters and about 5 millimeters. In otherembodiments, the aperture 494 may have a diameter of between about 1.5millimeters and about 2 millimeters.

A person of skill in the art will appreciate that it is possible toattach the second attachment section 64 and the cutting assembly 432using different structures, which enable sliding and rotating of thesecond attachment section 64 and the cutting assembly 432 with respectto the elongated shaft 40.

In one configuration, each of the cutting assembly strips 432 a, 432 bis formed into the wavy configuration and then the cutting assemblystrips 432 a, 432 b are attached to each other. The wave section 440 maybe positioned proximate the distal end of the cutting assembly strips432 a, 432 b.

In certain embodiments, the wave section 440 is located on between about30 percent and about 70 percent of the length of the cutting assemblystrips 432 a, 432 b. In other embodiments, the wave section 440 islocated on between about 50 and 60 percent of the length of the cuttingassembly strips 432 a, 432 b.

The length of the wave section 440 on the cutting assembly strips 432 a,432 b may be between about 10 millimeters and about 30 millimeters. Incertain embodiments, the length of the wave section 440 on the cuttingassembly strips 432 a, 432 b may be between about 15 millimeters andabout 20 millimeters.

There may be a spacing between the distal most wave and the distal endof the cutting assembly strip 432 a, 432 b. Forming the cutting assemblystrips 432 a, 432 b with this configuration provides the cuttingassembly 432 with a relatively flat distal end. This relatively flatdistal end may be used for guiding the cutting assembly 432 through thetissue between the ilium 14 and the sacrum 16, as opposed to allowingthe cutting assembly 432 to cut into the surface of the ilium 14 or thesacrum 16.

In certain embodiments, a spacing between the distal most wave and thedistal end of the cutting assembly strips 432 a, 432 b is between about1 millimeter and about 5 millimeters. In other embodiments, the spacingbetween the distal most wave and the distal end of the cutting assemblystrips 432 a, 432 b is between about 2 millimeters and about 3millimeters.

The number of waves 440 included on the cutting assembly strips 432 a,432 b may be determined by a variety of factors. Examples of thesefactors include the angle at which the cutting assembly strips 432 a,432 b may be bent without significantly impacting the strength of thecutting assembly strips 432 a, 432 b and without causing a sharp bendline to be formed between the ascending and descending portions of thecutting assembly strips 432 a, 432 b.

In certain embodiments, there are between 2 and 10 waves 440 formed inthe cutting assembly strips 432 a, 432 b. In other embodiments, thereare about four waves 440 formed in the cutting assembly strips 432 a,432 b. While it is illustrated that each of the waves 440 has asubstantially similar shape, it is possible to form the waves 440 havingdifferent shapes. For example, the waves 440 may have differing heightsand differing widths.

To increase the amount of tissue between the ilium 14 and the sacrum 16that can be cut using the cutting assembly 432, it may be desirable forthe waves 440 on the two adjacent cutting assembly strips 432 a, 432 bto have a height that is close to the distance between the ilium 14 andthe sacrum 16. Since the distance between the ilium 14 and the sacrum 16may vary at different locations in the sacroiliac joint, the height ofthe waves 440 may be selected based upon the minimum distance betweenthe ilium 14 and the sacrum 16.

Since there are two cutting assembly strips 432 a, 432 b used forfabricating the cutting assembly 432, the waves 440 on each of thecutting assembly strips 432 a, 432 b may have a maximum height that isless than about one-half of a distance between the surfaces of the ilium14 and the sacrum 16. Forming the waves 440 with the preceding maximumheight minimizes the potential that the upper portion 450 of the waves440 will be forced into the surface of the ilium 14 or the sacrum 16.

Since the ilium 14 and the sacrum 16 are formed from a material that isharder than the tissue between the ilium 14 and the sacrum 16, forcingthe upper portion 450 of the waves 440 into the surface of the ilium 14or the sacrum 16 will make it harder to operate the undercutting system.

In certain embodiments, a distance between the upper portion 450 and thelower portion 452 of the waves 440 on each of the cutting assemblystrips 432 a, 432 b will be between about 1 millimeter and about 3millimeters. In other embodiments, the distance between the upperportion 450 and the lower portion 452 of the waves 440 on each of thecutting assembly strips 432 a, 432 b may be about 1.75 millimeters.

A distance between the upper portions 450 of adjacent waves 440 may bebetween about 2 millimeters and about 6 millimeters. In certainembodiments, the distance between the upper portions 450 of adjacentwaves 440 may be about 4 millimeters.

While it is possible for the radius of curvature of the upper portions450 and the lower portions 452 of the waves to be substantially equal toeach other, in certain embodiments, the radius of curvature of the upperportions 450 of the waves 440 is greater than the radius of curvature ofthe lower portions 452 of the waves 440.

Forming the waves 440 with the radius of curvature of the upper portions450 being greater than the radius of curvature of the lower portions 452provides the upper portions 450 with a greater length than the lowerportions 452. This configuration increases the ability of the cuttingassembly 432 to cut tissue located between the ilium 14 and the sacrum16.

The radius of curvature of the upper portions 450 of the waves 440 maybe between about 0.30 millimeters and about 2 millimeters. In certainembodiments, the radius of curvature of the upper portions 450 of thewaves 440 is between about 0.80 millimeters and about 0.90 millimeters.

The radius of curvature of the lower portions 452 of the waves 440 maybe between about 0.30 millimeters and about 2 millimeters. In certainembodiments, the radius of curvature of the lower portions 452 of thewaves 440 is between about 0.50 millimeters and about 0.60 millimeters.

The waves 440 may be offset from the proximal end of the cuttingassembly strips 432 a, 432 b so that the proximal ends of two cuttingassembly strips 432 a, 432 b may be placed adjacent to each other whilethe lower portions 452 of the waves 440 on the adjacent cutting assemblystrips 432 a, 432 b are adjacent to each other.

In certain embodiments, the offset from the proximal end and the centerof the waves 440 that is intermediate the upper portion 450 and thelower portion 452 is between about 0.40 millimeters and about 2millimeters. In other embodiments, the offset from the proximal end andthe center of the waves 440 that is intermediate the upper portion 450and the lower portion 452 is between about 0.60 millimeters and about0.90 millimeters.

Similarly, the waves 440 may be offset from the distal end of thecutting assembly strip 432 a, 432 b so that the distal ends of twocutting assembly strips 432 a, 432 b may be placed adjacent to eachother while the lower portions 452 of the waves 440 on the adjacentcutting assembly strips 432 a, 432 b are adjacent to each other.

In certain embodiments, the offset from the distal end and the center ofthe waves 440 that is intermediate the upper portion 450 and the lowerportion 452 is between about 0.40 millimeters and about 2 millimeters.In other embodiments, the offset from the distal end and the center ofthe waves 440 that is intermediate the upper portion 450 and the lowerportion 452 is between about 0.60 millimeters and about 0.90millimeters.

The two cutting assembly strips 432 a, 432 b may be attached to eachother proximate the distal ends thereof. One suitable technique that maybe used for attaching the distal ends of the cutting assembly strips 432a, 432 b to each other is by welding. Laser welding is an example of onesuitable welding technique.

Since the proximal ends of the cutting assembly strips 432 a, 432 b areattached to the other portions of the undercutting system, it may not benecessary to attach the proximal ends of the cutting assembly strips 432a, 432 b to each other. Similarly, it may not be necessary to fasten thecutting assembly strips 432 a, 432 b to each other proximate the lowerportions 452 of the waves 440. Not attaching the proximal ends of thecutting assembly strips 432 a, 432 b and the lower portions 452 of thewaves 440 may increase the flexibility of the cutting assembly 432.

While it is possible to sharpen at least a portion of the side edges ofthe cutting assembly strips 432 a, 432 b to increase the ability of thecutting assembly 432 to cut the tissue between the ilium 14 and thesacrum 16, the cutting assembly 432 may be fabricated without sharpeningthe side edges of the cutting assembly strips 432 a, 432 b.

Even without sharpening, the side edges of the cutting assembly strips432 a, 432 b may be sufficiently sharp to cut the tissue between theilium 14 and the sacrum 16. If the side edges of the cutting assemblystrips 432 a, 432 b are sharpened, the side edges may be too sharp,which could make it more likely that the cutting assembly 432 would cutinto the ilium 14 and the sacrum 16.

Even though it is desired to prepare the surfaces of the ilium 14 andthe sacrum 16 with the undercutting system, it is generally desirable tonot cut too deeply into the ilium 14 and the sacrum 16, as such cuttingwould not only increase the time associated with preparing the ilium 14and the sacrum 16 for the sacroiliac fusion but could also negativelyimpact the strength of the ilium 14 and the sacrum 16.

The undercutting system may include a plurality of cutting assemblies432 having waves 440 with different heights. One of the cuttingassemblies 432 with having the smallest wave height may be initiallyused. Thereafter, cutting assemblies 432 having progressively largerwave heights may be used to form a progressively wider region betweenthe ilium 14 and the sacrum 16.

The cutting assembly strips 432 a, 432 b having the preceding shape andcharacteristics may be formed from a variety of materials. A person ofskill in the art will appreciate that the material used to fabricate thecutting assembly strips 432 a, 432 b should be suitable for use within ahuman body. An example of one such material for fabricating the cuttingassembly strips 432 a, 432 b is nitinol. A beneficial quality of nitinolis that nitinol is bendable but returns to the unbent configuration whenthe force that caused the bending is removed.

In another embodiment, the cutting assembly 532 may have a shape that isgenerally similar to the shape of the cutting assembly 432 illustratedin FIGS. 15-17. This cutting assembly 532 may include a single strip ofmaterial in which a plurality of waves 540 formed therein and in whichthe ends of the single strip of material are positioned adjacent to eachother so that the single strip of material is in a looped configuration,as illustrated in FIGS. 18-20.

The cutting assembly 532 may have a thickness of up to about 2millimeters. In certain embodiments, the cutting assembly 532 may have athickness of between about 0.1 millimeters and about 0.3 millimeters.Using the cutting assembly 532 with the preceding dimensions providesthe cutting assembly 532 with flexibility in a distal-proximal directionwhile resisting twisting or otherwise deforming.

The resistance enables the cutting assembly 532 to deflect in responseto changes in the shape or orientation of the ilium 14 or the sacrum 16.Such deflection is important because it is much more difficult to cutthrough the bone of the ilium 14 and the sacrum 16 than the cartilagethat is between the ilium 14 and the sacrum 16.

The configuration of the cutting assembly 532 provides the cuttingassembly 532 with sufficient rigidity in a radial direction. Such aconfiguration allows the cutting assembly 532 to resist deformation inresponse to rotation of the undercutting system during the cuttingprocess such as when the tissue between the ilium 14 and the sacrum 16is contacted with the cutting assembly 532.

The cutting assembly 532 may have a width that is no greater than aninner diameter of the elongated shaft 40. Forming the cutting assembly532 with such a configuration enables the cutting assembly 532 to bepositioned substantially within a profile of the elongated shaft 40 whenthe cutting assembly 532 is in a retracted configuration so that thecutting assembly 532 does not interfere with the insertion of the distalend of the undercutting system extending through the aperture 20 in theilium 14.

The cutting assembly 532 may have a width of between about 2 millimetersand about 5 millimeters. In certain embodiments, the cutting assembly532 may have a width of about 3 millimeters.

Side edges of the cutting assembly 532 may be sufficient to cut throughthe tissue between the ilium 14 and the sacrum 16. Using the cuttingassembly 532 without the sharpened edges may reduce a tendency of thecutting assembly 532 to cut into the ilium 14 and the sacrum 16 whilethe cutting assembly 532 is rotated.

Alternatively, the cutting assembly 532 may include a cutting surface onat least one edge thereof. In certain embodiments, cutting surfaces areprovided on both side edges of the cutting assembly 532. Providing thecutting surfaces on the side edges enhances the ability of the cuttingassembly 532 to cut the tissue between the ilium 14 and the sacrum 16while the cutting assembly 532 is rotated in clockwise and counterclockwise directions.

In certain embodiments, a distal end of the cutting assembly 532 may nothave a cutting surface. Forming the distal end without the cuttingsurface reduces a tendency of the cutting assembly 532 to cut into theilium 14 or the sacrum 16 as the cutting assembly 532 is a from theinsertion apparatus 30.

An aperture 594 may be formed in the proximal end of the cuttingassembly 532. The aperture 594 may have a diameter that is slightlylarger than a diameter of the attachment pin 92. Using such aconfiguration, the attachment pin 92 may extend into the aperture 594 toretain the cutting assembly 532 in a fixed relationship with respect tothe second attachment section 64.

The aperture 594 should not be too large such that the aperture 594weakens the cutting assembly 532, which could cause the cutting assembly532 to fail when a force is applied to the cutting assembly 532 such asoccurs during the use of the undercutting system to cut tissue frombetween the ilium 14 and the sacrum 16.

The aperture 594 may be generally circular and may have a diameter ofbetween about 0.5 millimeters and about 5 millimeters. In otherembodiments, the aperture 594 may have a diameter of between about 1.5millimeters and about 2 millimeters.

A person of skill in the art will appreciate that it is possible toattach the second attachment section 64 and the cutting assembly 532using different structures, which enable sliding and rotating of thesecond attachment section 64 and the cutting assembly 532 with respectto the elongated shaft 40.

In one configuration, the cutting assembly 532 is formed into the wavyconfiguration and then the cutting assembly 532 is bent in half. Thewave section 540 may be positioned proximate the distal end of thecutting assembly 532.

In certain embodiments, the wave section 540 is located on between about30 percent and about 70 percent of the length of the cutting assembly532. In other embodiments, the wave section 540 is located on betweenabout 50 and 60 percent of the length of the cutting assembly 532.

The length of the wave section 540 on the cutting assembly 532 may bebetween about 10 millimeters and about 30 millimeters. In certainembodiments, the length of the wave section 540 on the cutting assembly532 may be between about 15 millimeters and about 20 millimeters.

There may be a spacing between the distal most wave and the distal endof the cutting assembly 532. Forming the cutting assembly 532 with thisconfiguration provides the cutting assembly 532 with a relatively flatdistal end. This relatively flat distal end may be used for guiding thecutting assembly 532 through the tissue between the ilium 14 and thesacrum 16, as opposed to allowing the cutting assembly 532 to cut intothe surface of the ilium 14 or the sacrum 16.

In certain embodiments, a spacing between the distal most wave and thedistal end of the cutting assembly 532 is between about 1 millimeter andabout 5 millimeters. In other embodiments, the spacing between thedistal most wave and the distal end of the cutting assembly 532 isbetween about 2 millimeters and about 3 millimeters.

The number of waves 540 included on the cutting assembly 532 may bedetermined by a variety of factors. Examples of these factors includethe angle at which the cutting assembly 532 may be bent withoutsignificantly impacting the strength of the cutting assembly 532 andwithout causing a sharp bend line to be formed between the ascending anddescending portions of the cutting assembly 532.

In certain embodiments, there are between 2 and 10 waves 540 formed oneach side the cutting assembly 532. In other embodiments, there areabout four waves 540 formed on each side of the cutting assembly 532.While it is illustrated that each of the waves 540 has a substantiallysimilar shape, it is possible to formed the waves 540 having differentshapes. For example, the waves 540 may have differing heights anddiffering widths.

To increase the amount of tissue between the ilium 14 and the sacrum 16that can be cut using the cutting assembly 532, it may be desirable forthe waves 540 on the two sides of the cutting assembly 532 to have aheight that is close to the distance between the ilium 14 and the sacrum16. Since the distance between the ilium 14 and the sacrum 16 may varyat different locations in the sacroiliac joint, the height of the waves540 may be selected based upon the minimum distance between the ilium 14and the sacrum 16.

Since there are two sides of the cutting assembly 532 on which the waves540 are formed, the waves 540 on each side may have a maximum heightthat is less than about one-half of a distance between the surfaces ofthe ilium 14 and the sacrum 16. Forming the waves 540 with the precedingmaximum height minimizes the potential that the upper portion 550 of thewaves 540 will be forced into the surface of the ilium 14 or the sacrum16, as the cutting assembly 532 is rotated.

Since the ilium 14 and the sacrum 16 are formed from a material that isharder than the tissue between the ilium 14 and the sacrum 16, forcingthe upper portion 550 of the waves 540 into the surface of the ilium 14or the sacrum 16 will make it harder to operate the undercutting system.

In certain embodiments, a distance between the upper portion 550 and thelower portion 552 of the waves 540 on each side of the cutting assembly532 will be between about 1 millimeter and about 3 millimeters. In otherembodiments, the distance between the upper portion 550 and the lowerportion 552 of the waves 540 on each side of the cutting assembly 532may be about 1.75 millimeters.

A distance between the upper portions 550 of adjacent waves 540 may bebetween about 2 millimeters and about 6 millimeters. In certainembodiments, the distance between the upper portions 550 of adjacentwaves 540 may be about 4 millimeters.

While it is possible for the radius of curvature of the upper portions550 and the lower portions 552 of the waves to be substantially equal toeach other, in certain embodiments, the radius of curvature of the upperportions 550 of the waves 540 is greater than the radius of curvature ofthe lower portions 552 of the waves 540.

Forming the waves 540 with the radius of curvature of the upper portions550 being greater than the radius of curvature of the lower portions 552provides the upper portions 550 with a greater length than the lowerportions 552. This configuration increases the ability of the cuttingassembly 532 to cut tissue located between the ilium 14 and the sacrum16.

The radius of curvature of the upper portions 550 of the waves 540 maybe between about 0.30 millimeters and about 2 millimeters. In certainembodiments, the radius of curvature of the upper portions 550 of thewaves 540 is between about 0.80 millimeters and about 0.90 millimeters.

The radius of curvature of the lower portions 552 of the waves 540 maybe between about 0.30 millimeters and about 2 millimeters. In certainembodiments, the radius of curvature of the lower portions 552 of thewaves 540 is between about 0.50 millimeters and about 0.60 millimeters.

The waves 540 may be offset from the proximal end of the cuttingassembly 532 so that the proximal ends of the two sides of the cuttingassembly 532 may be placed adjacent to each other while the lowerportions 552 of the waves 540 on the two sides of the cutting assembly532 are adjacent to each other.

In certain embodiments, the offset from the proximal end and the centerof the waves 540 that is intermediate the upper portion 550 and thelower portion 552 is between about 0.40 millimeters and about 2millimeters. In other embodiments, the offset from the proximal end andthe center of the waves 540 that is intermediate the upper portion 550and the lower portion 552 is between about 0.60 millimeters and about0.90 millimeters.

Similarly, the waves 540 may be offset from the distal end of thecutting assembly 532 so that the distal end of two cutting assembly 532may be substantially flat while the lower portions 552 of the waves 540on the two sides of the cutting assembly 532 are adjacent to each other.

In certain embodiments, the offset from the distal end and the center ofthe waves 540 that is intermediate the upper portion 550 and the lowerportion 552 is between about 0.40 millimeters and about 2 millimeters.In other embodiments, the offset from the distal end and the center ofthe waves 540 that is intermediate the upper portion 550 and the lowerportion 552 is between about 0.60 millimeters and about 0.90millimeters.

Since the proximal ends of the two sides of the cutting assembly 532 areattached to the other portions of the undercutting system, it may not benecessary to attach the proximal ends of the two sides of the cuttingassembly 532 to each other. Similarly, it may not be necessary to fastenthe two sides of the cutting assembly 532 to each other proximate thelower portions 552 of the waves 540. Not attaching the proximal ends ofthe two sides of the cutting assembly 532 and the lower portions 552 ofthe waves 540 of the two sides of the cutting assembly 532 may increasethe flexibility of the cutting assembly 532.

While it is possible to sharpen at least a portion of the side edges ofthe cutting assembly 532 to increase the ability of the cutting assembly532 to cut the tissue between the ilium 14 and the sacrum 16, thecutting assembly 532 may be fabricated without sharpening the side edgesof the cutting assembly 532.

Even without sharpening, the side edges of the cutting assembly 532 maybe sufficiently sharp to cut the tissue between the ilium 14 and thesacrum 16. If the side edges of the cutting assembly 532 are sharpened,the side edges may be too sharp, which could make it more likely thatthe cutting assembly 532 would cut into the ilium 14 and the sacrum 16.

Even though it is desired to prepare the surfaces of the ilium 14 andthe sacrum 16 with the undercutting system, it is generally desirable tonot cut too deeply into the ilium 14 and the sacrum 16, as such cuttingwould not only increase the time associated with preparing the ilium 14and the sacrum 16 for the sacroiliac fusion but could also negativelyimpact the strength of the ilium 14 and the sacrum 16.

The undercutting system may include a plurality of cutting assemblies532 having waves 540 of different heights. One of the cutting assemblies532 with having the smallest wave height may be initially used.Thereafter, cutting assemblies 532 having progressively larger waveheight may be used to form a progressively wider region between theilium 14 and the sacrum 16.

The cutting assembly 532 having the preceding shape and characteristicsmay be formed from a variety of materials. A person of skill in the artwill appreciate that the material used to fabricate the cutting assembly532 should be suitable for use within a human body. An example of onesuch material for fabricating the cutting assembly 532 is nitinol. Abeneficial quality of nitinol is that nitinol is bendable but returns tothe unbent configuration when the force that caused the bending isremoved.

In another embodiment, the undercutting system 610, may include aninsertion apparatus 630 and a probe assembly 632 that extends from adistal end of the insertion apparatus 630, as illustrated in FIGS.21-25.

The insertion apparatus 630 may include an elongated shaft 640 that isformed with a length that enables a proximal end thereof to bepositioned outside of the patient's body while a distal end thereof isutilized to the prepare the region between the ilium 14 and the sacrum16 for the sacroiliac fusion process. In certain embodiments, the lengthof the elongated shaft 640 is between about 15 centimeters and about 45centimeters.

The elongated shaft 640 may be formed with a relatively small outerdiameter to minimize a size of the aperture 20 that needs to be formedin the ilium 14. The larger the aperture 20 that is formed in the ilium14, the greater the potential of the ilium 14 weakening to the point atwhich the ilium 14 is more susceptible to breakage. In certainembodiments, the outer diameter of the elongated shaft 640 is betweenabout 6 millimeters and 20 millimeters.

The insertion apparatus 630 may also include a handle portion 642proximate a proximal end thereof. The handle portion 642 enhances theability to manipulate the insertion apparatus 630 such as insertion,rotation and withdrawal.

The handle portion 642 may have a diameter that is greater than adiameter of the elongated shaft 640. In certain embodiments, the handleportion 642 has a diameter of between about 2 centimeters and about 20centimeters.

An outer edge of the handle portion 642 may have a plurality of concaveregions 644 formed therein. The concave regions 644 enhance the abilityto grip the handle portion 642 and thereby manipulate the insertionapparatus 630.

The insertion apparatus 630 may further include a control knob 646 thatis used for extending and retracting the probe assembly 362. In oneconfiguration of the insertion apparatus 630, the control knob 646 isrotatably mounted with respect to the insertion apparatus 630.

The control knob 646 may have a diameter that is different than adiameter of the handle portion 642. Forming the control knob 646 with adiameter that is different than a diameter of the handle portion 642minimizes the potential that a person using the insertion apparatus 630would inadvertently manipulate the insertion apparatus 630 or thecontrol knob 646.

The control knob 646 may have a diameter that is less than a diameter ofthe handle portion 642. In certain embodiments, the control knob 646 hasa diameter of between about 2 centimeters and about 20 centimeters.

An outer edge of the control knob 646 may have a plurality of concaveregions (not shown) formed therein. The concave regions enhance theability to grip the control knob 646 and thereby manipulate theinsertion apparatus 630.

Rotation of the control knob 646 in a first direction causes the probeassembly 632 to be extended from the distal end of the insertionapparatus 630. Rotation of the control knob 646 in a second direction,which is opposite the first direction, causes the probe assembly 632 tobe retracted into the distal end of the insertion apparatus 630.

The insertion apparatus 630 may also include a lock screw 650 operablyattached hereto. The lock screw 650 may be oriented generally transverseto the elongated shaft 40 and may be positioned proximate the handleportion 642. The lock screw 650 may threadably engage the elongatedshaft 640.

The lock screw 650 may be positioned in an engaged position where adistal end of the lock screw 650 extends into the interior of theelongated shaft 640 until the distal end engages a shaft that extendsbetween the probe assembly 632 and the control knob 646. The lock screw650 thereby retains the shaft in a fixed position with respect to theelongated shaft 640 to prevent movement of the probe assembly 632 withrespect to the insertion apparatus 630.

Rotating the lock screw 650 in an opposite direction causes the distalend to not engage the cutter shaft so that the shaft may be moved withrespect to the elongated shaft 640 to move the probe assembly 632between the extended and retracted positions.

Inside at least a portion of the elongated shaft 640 is a controlmechanism 660 that operably attaches the probe assembly 632 to the otherportions of the insertion apparatus 630, as most clearly illustrated inFIGS. 22, 24 and 25. A primary function of the control mechanism 660 isto facilitate extension and refraction of the probe assembly 632.

The control mechanism 660 may generally include a first attachmentsection 662 and a second attachment section 664. The first attachmentsection 662 is attached to the control knob 646. In one configuration,the first attachment section 662 is fixedly attached to the control knob646 so that the first section 662 rotates when the control knob 646 isrotated.

The first attachment section 662 may have a length that is less than thelength of the elongated shaft 640. In certain embodiments, the firstattachment section 662 has a length that is approximately one-half ofthe length of the elongated shaft 640.

The first attachment section 662 may have a generally cylindrical shapewith an outer diameter that is slightly smaller than an inner diameterof the elongated shaft 640, as most clearly illustrated in FIG. 22.Forming the first attachment section 662 with this shape facilitatesrotating and sliding of the first attachment section 662 with respect tothe elongated shaft 640.

A distal end of the first attachment section 662 has a connectionmechanism 666 that facilitates attaching the second attachment section664 to the first attachment section 662. In one such configuration, theconnection mechanism 666 includes a recess 670 formed in the distal end.The recess 670 may have a width and a depth that is greater that a widthand a depth of the proximal end of the second attachment section 664.

An attachment pin 672 may be provided in the recess 670 that enables thesecond attachment section 664 to engage the connection mechanism 666. Incertain embodiments, the attachment pin may be oriented generallyperpendicular to the first attachment section 662.

An aperture may be formed in the proximal end of the second attachmentsection 664. The aperture may have a diameter that is slightly largerthan a diameter of the attachment pin. Using such a configuration, theattachment pin may extend into the aperture to retain the firstattachment section 662 in a fixed relationship with respect to thesecond attachment section 664.

Forming the connection mechanism 666 with preceding configuration allowsthe second attachment section 664 to be attached to the first attachmentsection 662 when the first attachment section 662 and the secondattachment section 664 are not covered by the elongated shaft 640.

On the other hand, when the elongated shaft 640 is placed over firstattachment section 662 and the second attachment section 664, the secondattachment section 664 is retained in engagement with the firstattachment section 662.

A person of skill in the art will appreciate that it is possible toattach the first attachment section 662 and the second attachmentsection 664 using different structures, which enable sliding androtating of the first attachment section 662 and the second attachmentsection 664 with respect to the elongated shaft 640.

While the figures illustrate that a mechanical connection is providedbetween the probe assembly 632 and the other components of theundercutting system 610, it is also possible to utilize an electricalconnection between the probe assembly 632 and the other components ofthe undercutting system 610. Such an electrical connection may utilizeswitches and actuators. It is also possible to use pneumatic andhydraulic systems to operably connect the probe assembly 632 and theother components of the undercutting system 610.

The connection mechanism 666 may also include a ball-type connector 680that attaches the connection mechanism 666 to the first attachmentsection 662. The ball-type connector 680 may include a ball-shapedextension 682 on the connection mechanism 666 and a recess 684 formed inthe distal end of the first attachment section 662. The recess 684 has ashape that is generally complementary to the shape of the ball-shapedextension 682.

Similar to the attachment between the connection mechanism 666 and thesecond attachment section 664, the ball-type connector 680 allows thefirst attachment section 662 to be attached to the connection mechanism666 when the first attachment section 662 and the connection mechanism666 are not covered by the elongated shaft 640.

On the other hand, when the elongated shaft 640 is placed over firstattachment section 662 and the connection mechanism 666, the ball-shapedextension 682 is retained in engagement with the recess 684.

The probe assembly 632 is attached to the distal end of the secondattachment section 664. To accommodate using probe assemblies 632 havingdifferent lengths, the undercutting system 610 may be provided with morethan one second attachment section 664 having different lengths.Alternatively or additionally, the undercutting system 610 may includemore than one first attachment section 662 having different lengths.Using such a configuration enables one of the first attachment sections662 and the second attachment sections 664 to be selected based upon thelength of the probe assembly 632.

A benefit of using the ball-shaped extension 682 is that this connectionmechanism enables the control handle to rotate such as when extending orretracting the probe assembly 632 with respect to the insertionapparatus 630 without having the probe assembly 632 rotate.

The distal end of the second attachment section 664 may have a recessformed therein. The recess may have a depth that is greater than athickness of the proximal end of the probe assembly 632. The recess mayextend across at least a portion of a width of the second attachmentsection 664.

An attachment pin may be provided in the recess that enables the probeassembly 632 to engage the second attachment section 664. In certainembodiments, the attachment pin may be oriented generally perpendicularto the second attachment section 664.

The second attachment section 664 may be formed with a height and awidth that are both slightly smaller than a height and a width of achannel 696 that is formed in an end cap 700, which is discussed in moredetail below. Forming the second attachment section 664 with thesedimensions enables the second attachment section 664 to slide in thechannel 696.

The cap 700 may be positioned in the distal end of the elongated shaft640, as most clearly illustrated in FIG. 22. The cap 700 thereby sealsthe elongated shaft 640 to generally restrict tissue and fluid fromentering the elongated shaft 640.

While it is possible for a distal end of the cap 700 to be orientedgenerally transverse to the elongated shaft 640, the distal end of thecap 700 may be oriented at an angle of less than about 90 degrees withrespect to the elongated shaft 640. In certain embodiments, the distalend of the cap 700 is oriented at an angle of between about 45 degreesand about 60 degrees.

As referenced above, the cap 700 has the channel 696 formed therein.Proximate the proximal end, the channel 696 may be generally alignedwith but offset from a central axis of the elongated shaft 640.Proximate the distal end, the channel 696 may be oriented generallyperpendicular to the central axis of the elongated shaft 640.

Intermediate the proximal end and the distal end, the channel 696 iscurved. The radius of curvature may be determined by a variety offactors. An example of one such factor is the flexibility of the portionof the probe assembly 632 and the flexibility of the cutting assembly633.

The channel 696 thereby causes the probe assembly 632 to be deflectedsuch that when the probe assembly 632 extends from the cap 700, theprobe assembly 632 is oriented in a direction that is generallytransverse to the elongated shaft 640, as illustrated in FIG. 22, sothat the probe assembly 632 can be extended into the region between theilium 14 and the sacrum 16.

Because of the flexibility of the probe assembly 632, it is notnecessary that the distal end of the channel 696 be oriented preciselytransverse to the central axis of the elongated shaft 640. For example,the distal end of the channel 696 may be oriented slightly towards theilium 14 to encourage preferential cutting of the ilium 14 because theilium 14 is harder than the sacrum 16. Alternatively, orienting thedistal end of the channel 696 slightly towards the sacrum 16 may allowthe angle of curvature within the cap to be reduced.

The cap 700 may have an aperture that extends therethrough that isgenerally perpendicular to the axis of the elongated shaft 640. Theelongated shaft 640 may also include an aperture that is generallyaligned with the aperture when the cap 700 is placed into the distal endof the elongated shaft 640. A pin is extended through the aperture andthe aperture to thereby retain the cap 700 in a stationary position withrespect to the elongated shaft 640.

The cutting assembly 633 may be used in conjunction with the probeassembly 632. To permit the deflection of the cutting assembly 633, thecutting assembly 633 may be fabricated from a flexible material, as isdiscussed in more detail below. To increase the flexibility of thecutting assembly 633, a plurality of kerfs or notches 642 may be formedin the cutting assembly 633.

As illustrated in FIGS. 26-29, the kerfs 642 may extend through an uppersurface 650 of the cutting assembly 633. The kerfs 642 may also extendthrough at least a portion of at least one of the side surfaces 652 ofthe cutting assembly 633. The kerfs 642 may also extend into a portionof the lower surface 654 of the cutting assembly 633.

Forming the kerfs 642 with the preceding configuration allows a lowersurface 654 of the cutting assembly 633 to be substantially continuous.This configuration provides the cutting assembly 633 with sufficientstrength to resist breaking while the cutting assembly 633 is used tocut tissue from between the ilium 14 and the sacrum 16.

The kerfs 642 may be formed with a width that is sufficiently large sothat the opposite sides of each of the kerfs 642 do not contact eachother while the cutting assembly 633 is deflected from the initialorientation that is generally aligned with but offset from the centeraxis of the insertion apparatus 630 to a deflected orientation that isgenerally transverse to the central axis of the insertion apparatus, asthe cutting assembly 633 exits the distal end of the cap 700.

In certain embodiments, the kerfs 642 may have a width of up to about 1millimeter. In other embodiments, the kerfs 642 may have a width that isbetween about 0.4 millimeters and about 0.6 millimeters.

The kerfs 642 also decrease the smoothness of the cutting assembly 633.Contact between the kerfs 642 and the tissue between the ilium 14 andthe sacrum 16 could cause such tissue to be abraded or cut and therebyfacilitate preparation of the region between the ilium 14 and the sacrum16 for the sacroiliac fusion process.

While the figures illustrate that the kerfs 642 are formed on one sideof the cutting assembly 633, it is possible for the kerfs 642 to beformed on both sides of the cutting assembly 633. If the kerfs 642 areformed on both sides of the cutting assembly 633, the kerfs 642 on theopposite sides may be offset so that the kerfs 642 do not unduly weakenthe cutting assembly 633.

Whether the kerfs 642 are formed in one side or both sides of thecutting assembly 633, the kerfs 642 should not occupy too great aportion of the cutting assembly 633 such that the cutting assembly 633is likely to bend or kink during the process of deflecting during theextension or retraction of the cutting assembly 633 from the insertionapparatus 630 as well as during the use of the cutting assembly 633 tocut tissue from between the ilium 14 and the sacrum 16.

Depending on the material from which the cutting assembly 633 is formed,it may be possible to use other techniques that provide the cuttingassembly 633 with a desired degree of flexibility.

In addition to or as an alternative to kerfs for roughening the outersurface of the cutting assembly 633, it is possible to use othertechniques to enhance the ability of the cutting assembly 633 to cutthrough tissue between the ilium and the sacrum as well as to cut intothe ilium and the sacrum. An example of one such technique that may beused to roughen the outer surface of the cutting assembly 633 is toprovide an abrasive on at least a portion of the outer surface of thecutting assembly 633.

However, it should be noted that the fact that the cutting assembly 633may be supported by the probe assembly 632, which extends through thebore 640 in the cutting assembly 633.

The cutting assembly 633 having the preceding shape and characteristicsmay be formed from a variety of materials. A person of skill in the artwill appreciate that the material used to fabricate the cutting assembly633 should be suitable for use within a human body. An example of onesuch material for fabricating the cutting assembly 633 is nitinol. Abeneficial quality of nitinol is that nitinol is bendable but returns tothe unbent configuration when the force that caused the bending isremoved.

At least one cutting element 634 may be provided on the cutting assembly634. The cutting element 634 may be positioned proximate the distal endof the cutting assembly 633. In certain embodiments, the cutting element634 may include a main cutter portion 660 and at least one extensionportion 662 that extends from the main cutter portion 660.

The main cutter portion 660 may have a height that is greater than theheight of the cutting assembly 634. The main cutter portion 660 therebyenables a region between the ilium 14 and the sacrum 16 having a greaterthickness to be prepared.

The main cutter portion 660 may have a height that is no greater than aninner diameter of the elongated shaft 640. Forming the main cutterportion 660 with such a configuration enables the cutting assembly 633to be positioned substantially within a profile of the elongated shaft640 when the cutting assembly 633 is in a retracted configuration sothat the cutting assembly 633 does not interfere with the insertion ofthe distal end of the undercutting system 610 extending through theaperture 20 in the ilium 14.

The main cutter portion 660 may have a height of between about 1millimeter and about 3 millimeters. In certain embodiments, the maincutter portion 660 may have a width of about 2 millimeters.

Similarly, the main cutter portion 660 may have a width that is nogreater than an inner diameter of the elongated shaft 640. Forming themain cutter portion 660 with such a configuration enables the cuttingassembly 633 to be positioned substantially within a profile of theelongated shaft 640 when the cutting assembly 633 is in a retractedconfiguration so that the cutting assembly 633 does not interfere withthe insertion of the distal end of the undercutting system 610 extendingthrough the aperture 20 in the ilium 14.

The main cutter portion 660 may have a width of between about 2millimeters and about 5 millimeters. In certain embodiments, the maincutter portion 660 may have a width of about 3 millimeters.

The main cutter portion 660 may extend along at least a portion of theupper surface 650 and the lower surface 654. In certain embodiments, themain cutter portion 660 extends substantially around the entire cuttingassembly 633.

The main cutter portion 660 may be curved proximate each of the cornersthereof. Using the curved corners reduces the potential of the maincutter portion 660 digging into the surface of the ilium 14 or thesacrum 16 while the cutting assembly 633 is rotated.

In other embodiments, where it is desired to enhance the cutting abilityof the cutting assembly 633, the main cutter portion 660 may be formedwith sharp corners and at least a portion of the surface of the cornersmay be sharpened to enhance the cutting ability of the main cutterportion 660.

The main cutter portion 660 has a distal edge and a proximal edge thatare disposed at opposite ends thereof. In certain embodiments, thedistal edge and the proximal edge may be sufficiently sharp to cutthrough the tissue between the ilium 14 and the sacrum 16 that comesinto contact with at least one of the distal edge and the proximal edge.

Alternatively, at least one of the distal edge and the proximal edge mayinclude a cutting surface. In certain embodiments, cutting surfaces areprovided on both distal and proximal edges of the main cutter portion660. Providing the cutting surfaces on the distal and proximal edgesenhances the ability of the main cutter portion 660 to cut throughtissue between the ilium 14 and the sacrum 16 as the cutting assembly633 is rotated.

The extension portion 662 may have a generally planar configuration thatextends from at least one of the upper and lower surfaces of the maincutter portion 660. While not illustrated, it is also possible for atleast one of the extension portions 662 to be positioned on the sidesurfaces of the main cutter portion 660.

In certain embodiments, the extension portion 662 may extend insubstantially equal distances on opposite sides of the main cutterportion 660. The extension portion 662 may have a generally rectangularshape that is defined by a distal edge 670 and a pair of side edges 672.

While it is illustrated that a height of the extension portion 662 isapproximately equal on opposite sides of the main cutter portion 660, itis possible to configure the extension portion 662 so that the height ofthe extension portion 662 is not approximately equal on opposite sidesof the main cutter portion 660.

The height of the distal edge 670 may be limited by the inner diameterof the elongated shaft 40 so that the cutting element 634 may beretracted within the insertion apparatus 630 when the insertionapparatus 630 is inserted into and removed from the region between theilium 14 and the sacrum 16.

In certain embodiments, the height of the extension portion 662 onopposite sides of the main cutter portion 660 is between about 1millimeter and about 5 millimeters. In other embodiments, the height ofthe extension portion 662 on opposite sides of the main cutter portion660 is about 3 millimeters.

In certain embodiments, a width of the extension portion 662 isapproximately the same on opposite sides of the main cutter portion 660.The width of the extension portion 662 may be between about 1 millimeterand about 5 millimeters. In other embodiments, the width of theextension portion 662 is about 3 millimeters.

Corners proximate the intersection of the distal edge 670 and each ofthe side edges 672 may be curved. While such curvature could reduce thecutting ability of the extension portion 662 that could be attained ifthe distal edge 670 and the side edge 672 intersected at a corner, thiscurvature may reduce the tendency of the extension portion 662 to digtoo deeply into the surfaces of the ilium 14 and the sacrum 16. As aresult of this configuration, the extension portion 662 wouldpreferentially cut into the tissue between the ilium 14 and the sacrum16 as opposed to cutting the ilium 14 and the sacrum 16.

While it is illustrated that the extension portion 662 has asubstantially equal thickness, it is possible for the thickness of theextension portion 662 to vary. In certain embodiments, the thickness ofthe extension portion 662 may be greater proximate to the main cutterportion 660 to resist bending or deformation of the cutting element 634.

In certain embodiments, a thickness of the extension portion 662 may bebetween about 0.2 millimeters and about 2 millimeters. In otherembodiments, the thickness of the extension portion 662 may be about 0.5millimeters.

While it is illustrated that the thickness of the extension portion 662is approximately equal on opposite sides of the main cutter portion 660,it is possible to configure the extension portion 662 so that thethickness of the extension portion 662 is not approximately equal onopposite sides of the main cutter portion 660.

The edge of the extension portion 662 proximate the distal ends thereofmay be sufficient to cut through the tissue between the ilium 14 and thesacrum 16. Using the extension portion 662 without the sharpened edgesmay reduce a tendency of the extension portion 662 to cut into the ilium14 and the sacrum 16 while the cutting assembly 633 is rotated.

Alternatively, the edge of the extension portion 662 proximate thedistal ends thereof may be sharpened to facilitate cutting of tissueproximate the surfaces of the ilium 14 and the sacrum 16 while thecutting assembly 633 is rotated.

The extension portion 662 may be oriented generally parallel to thelength of the cutting element 634, as illustrated in FIGS. 26-28. Inother embodiments, the extension portion 662 may be oriented at an angleof between about 0 degrees and about 60 degrees with respect to a lengthof the cutting element 634, as illustrated in FIG. 29. In otherembodiments, the angle between the extension portion 662 and the maincutter portion 660 may be about 30 degrees.

Orienting the extension portion 662 at the angle with respect to thelength of the main cutter portion 660 causes one of the edges to bedisposed forwardly. Such a configuration may increase the ability of thecutting element 634 to cut tissue from between the ilium 14 and thesacrum 16 as the cutting assembly 634 is rotated.

While it is illustrated that the extension portion 662 is orientedgenerally transverse to the surface of the main cutter portion 660, itis possible for the extension portion 662 to be oriented at an anglewith respect to the surface of the main cutter portion 660.

While it is possible for the cutting element 634 to be placed at thedistal end of the cutting assembly 633, in certain embodiments, thecutting element 634 is mounted a distance from the distal end of thecutting assembly 633. Mounting the cutting element 634 a distance fromthe distal end of the cutting assembly 633 enables the cutting assembly633 to define a path through the tissue between the ilium 14 and thesacrum 16, as opposed to the cutting element 634 being the primarycomponent that defines the path through the tissue between the ilium 14and the sacrum 16.

The extension portion 662 may be positioned at a location that isapproximately intermediate between the side edges of the main cutterportion 660. Placing the extension portion 662 in this location mayreduce twisting of the cutting assembly 633, which could potentiallyoccur if the extension portion 662 was located closer to one of the sideedges of the main cutter portion 660.

The cutting element 634 having the preceding shape and characteristicsmay be formed from a variety of materials. A person of skill in the artwill appreciate that the material used to fabricate the cutting element634 should be suitable for use within a human body. An example of onesuch material for fabricating the cutting element 634 is nitinol.

In certain embodiments, the cutting assembly 633 may be fabricatedseparately from the cutting element 634. Forming the structure in thismanner enables different materials to be used for fabricating thecutting assembly 633 and the cutting element 634 so that the respectivematerials may be optimized based upon the function of the associatedstructure.

The cutting element 634 may be attached to the cutting assembly 633using a variety of techniques that cause the cutting element 634 to befixedly attached to the cutting assembly 633. One such suitabletechnique for attaching the cutting element 634 to the cutting assembly633 is welding.

Alternatively, it is possible to fabricate the cutting assembly 633 andthe cutting element 634 as a single unit such as by machining a block toprovide a substantially flat cutting assembly 633 and a cutting element634 that extends from the cutting assembly 633.

The undercutting system 610 may include a plurality of cuttingassemblies 632 with cutting elements 634 having different distancesthickness. One of the cutting assemblies 632 with the cutting element634 having the smallest thickness may be initially used. Thereafter,cutting assemblies 632 with cutting elements 634 having progressivelylarger thicknesses may be used to form a progressively wider regionbetween the ilium and the sacrum.

In addition to or in an alternative to forming the cutting elements 634with different thicknesses, it is possible to use a series of cuttingelements 634 to facilitate preparing the surfaces of the ilium 14 andthe sacrum 16 in a predictable manner. In one such configuration, thereis a series of three cutting elements 634 used to prepare the regionbetween the ilium 14 and the sacrum 16.

The first cutting element 634 may be configured to preferentially cuttissue on the ilial side of the first cutting element 634. The firstcutting element 634 may have one extension portion 662 that ispositioned on the ilial side of the first cutting element 634.

The extension portion 662 may have a first height that extends above asurface thereof. In certain embodiments, the extension portion 662 mayhave a height of about 0.5 millimeters. The overall height of the firstcutting element 634 is thereby about 2.5 millimeters.

Because the extension portion 662 is on the ilial side of the firstcutting element 634, this configuration may exhibit beneficialperformance characteristics because this configuration accounts for thefact that a surface of the ilium 14 is harder than a surface of thesacrum 16.

The second cutting element 634 may also include one extension portion662 that is positioned on the ilial side of the first cutting element634. The extension portion 662 on the second cutting element 634 mayhave a height that is greater than the height of the extension portion662 on the first cutting element.

The extension portion 662 may have a second height that extends above asurface thereof. In certain embodiments, the extension portion 662 mayhave a height of about 1 millimeter. The overall height of the firstcutting element 634 is thereby about 3 millimeters.

The configuration of the second cutting element 634 thereby enables anincreased distance area between the ilium 14 and the sacrum 16 to beprepared, as compared to the first cutting element 634. However, similarto the first cutting element 634, the second cutting element 634preferentially cuts on the ilial side of the second cutting element 634.

The third cutting element 634 may have an extension portion 662 that ispositioned on the ilial and sacral sides thereof. While it is possiblefor the extension portions 662 to have different heights, in certainembodiments, the extension portions 662 each have a height of about 1millimeter. The overall height of the third cutting element 634 isthereby about 4 millimeters.

Because the extension portions 662 are positioned on the ilial andsacral sides of the third cutting element 634, the third cutting elementcuts tissue that is located on the ilial and sacral side of the thirdcutting element 634.

The cutting assembly 633 may be operably attached to the insertionapparatus 630 to facilitate extension and refraction of the cuttingassembly 633 with respect to the insertion apparatus 630. In oneembodiment, a control is provided for movement of the cutting assembly132 that is separate from the control knob 646 used to move the probeassembly 632.

The cutting assembly control may be a knob 676 that is mounted to theinsertion apparatus. Similar to the control knob 646, rotation of thecutting assembly control knob 676 in a first direction may causeextension of the cutting assembly 633 from the insertion apparatus 630and rotation of the cutting assembly control knob 676 in a seconddirection may cause retraction of the cutting assembly 633 into theinsertion apparatus 630.

In another embodiment, the probe assembly 632 and the cutting assembly633 are both operably connected to the control knob 646. When thecontrol knob 646 is initially rotated, the probe assembly 632 isextended progressively further from the insertion apparatus 630. Oncethe probe assembly 632 reaches its maximum extension, continued rotationof the control knob 646 causes the cutting assembly 633 to be extendedfrom the insertion apparatus 630.

When the surgical procedure is completed and it is desired to remove theundercutting system, the control knob 646 is rotated in an oppositedirection. This rotation initially causes retraction of the cuttingassembly 633.

As illustrated in FIGS. 26-28, the distal end of the probe assembly 632extends beyond the distal end of the cutting assembly 633 when thesecomponents are extended from the distal end of the insertion apparatus630. Using this configuration enables the probe assembly 632 to guidethe cutting assembly 633 and thereby reduce the potential of the cuttingassembly 633 digging too deeply into the ilium 14 or the sacrum 16.

Once the probe assembly 632 has been extended the maximum distance fromthe distal end of the insertion apparatus 630 and the insertionapparatus 630 has been rotated at least one full revolution so that theprobe assembly 632 has caused the path between the ilium 14 and thesacrum 16 to be defined, it may be possible for the cutting assembly 633to be fully extended so that the distal end of the cutting assembly 633is at approximately the same distance from the distal end of theinsertion apparatus 630 as the probe assembly 632.

Once the cutting assembly 633 is fully retracted, continued rotation ofthe control knob 46 causes the probe assembly 632 to be retracted. Afterboth the probe assembly 632 and the cutting assembly 633 are fullyrefracted within the insertion apparatus 630, the undercutting systemmay be removed from the patient.

Using the probe assembly 632 in conjunction with the cutting assembly633 enables the region between the ilium 14 and the sacrum 16 to beprepared for the sacroiliac fusion while minimizing the cutting assembly633 digging into the surface of the ilium 14 or the sacrum 16.

While it is desirable to prepare the surfaces of the ilium 14 and thesacrum 16 by exposing bleeding bone, it is desirable to avoid thecutting assembly 633 digging into the surface of the ilium 14 or thesacrum 16 too deeply. When the cutting assembly 633 digs too deeply intothe surface of the ilium 14 or the sacrum 16, it becomes more difficultto rotate the cutting assembly 633 because the ilium 14 and the sacrum16 are much harder than the tissue located between the ilium 14 and thesacrum 16. The cutting assembly 633 having the characteristics set forthabove meets these criteria.

To minimize the potential of the cutting assembly breaking during thecutting process, a clutch mechanism may be provided between the handleand the cutting assembly. The clutch mechanism causes the operableconnection between the handle and the cutting assembly to release whengreater than a threshold force is encountered. When this occurs, thehandle rotates with respect to the cutting assembly.

An audible notification may be provided to indicate to the personoperating the cutting assembly that the clutch has been engaged. Anexample of which such audible notification is a scratching sound that issufficiently loud to be heard outside of the patient.

After the clutch has been activated, the person operating the cuttingassembly may rotate the cutting assembly in an opposite direction orpartially retract the cutting assembly. Thereafter, the cutting processmay be resumed.

In operation, to facilitate use of the undercutting system 10 and theperformance of the sacroiliac fusion, the patient on which thesacroiliac fusion is to be performed may be positioned in a proneorientation on an operating room table or other support structure thatis used in conjunction with this procedure.

While it is possible to form a relatively large incision and then pullback the tissue between the skin and the ilium so that the surface ofthe ilium could directly be viewed when using the undercutting system 10of the invention, such a process could cause more damage to the tissuebetween the skin and the ilium, which could increase the time for thepatient to recover from the surgical procedure.

The tissue penetrated when using the method discussed herein may include(when moving from lateral to medial)—skin, gluteus maximus, gluteusmedius, gluteus minimus, lateral ilium cortex, medial ilium cortex,sacroiliac joint cartilage (ilium and sacrum), lateral sacral cortex,sacral ala, sacral vestibule (which is also known as alar root, sacralpedicle and sacral isthmus) and sacral vertebral body.

Other critical soft tissue that is proximate to where the undercuttingsystem 10 is being used may include (when moving from lateral tomedial)—superior cluneal nerves, superior gluteal artery and vein, L4,L5, S1 and S2 nerve roots, iliac artery, iliac vein, sacral foris alsoknown as neuroforamina), bowels and sacral canal.

Additional relevant anatomical landmarks that have not been previouslymentioned include greater sciatic notch, alar slope and iliac corticaldensity, sacral prominence, pubic symphysis, pelvic brim/arcuate lineand S1 end plate.

After appropriate preparation of the patient and identification of thelocation for the sacroiliac fusion, at least one aperture 20 is drilledthrough the ilium 14. This aperture 20 may also at least partiallyextend into the sacrum 16, as illustrated in FIG. 30. In certainembodiments, there are three apertures drilled.

In certain embodiments, the aperture 20 is oriented generally transverseto the ilium 14, as illustrated in FIG. 30. In other embodiments, anangle between the aperture 20 and the ilium 14 may be between about 45°and about 135°. Fluoroscopic imaging may be used to determine theorientation of the aperture 20.

Orienting the aperture 20 at an angle in the preceding range limits thebending of the probe assembly 632 and the cutting assembly 633 if anglesgreater to or less than the preceding range were used. Using such angleswould require the probe assembly 632 and the cutting assembly 633 to beformed from a more flexible material.

Even though FIGS. 30-33 illustrate that the procedure is performed byinitially drilling into the ilium 14, it is also possible to perform thesacroiliac fusion by initially drilling into the sacrum 16. In certaincircumstances, it may present fewer challenges in gaining access for thesacroiliac fusion by initially drilling into the ilium 14.

A conventional surgical drill 710 and drill bit 712 may be utilized toform the aperture 20. The aperture 20 may be formed with a diameter thatis selected based upon a diameter of the bone screw 620 that will beinserted into the aperture 20 as part of the sacroiliac fusion process.

As illustrated in FIG. 30, the drill may be oriented generallytransverse to a surface of at least one of the ilium 14 and the sacrum16 proximate to where the aperture 20 is being formed. A person of skillin the art will appreciate that neither the sacrum 16 nor the ilium 14are substantially flat. Additionally, the adjacent surfaces of the ilium14 and the sacrum 16 may not be substantially parallel to each otherproximate to where it is desired to form the aperture 20.

The apertures 20 may include a first aperture 20 a that is used inconjunction with a first screw having a diameter of about 12.5millimeters. In this situation, the drill bit used to form the firstaperture 20 a may have a diameter of approximately 9 millimeters.

The first aperture 20 a may be formed across the sacroiliac joint at theS1 level. The first aperture 20 a may be positioned to favor ananterior-inferior side of the sacroiliac joint. The first aperture 20 amay be oriented at an angle so that the distal end of the first screw isslightly posterior and superior of a proximal end of the first screw.

The apertures 20 may also include a second aperture 20 b that is used inconjunction with a second screw having a diameter of about 6.5millimeters. In this situation, the drill bit used to form the secondaperture 20 b may have a diameter of approximately 5 millimeters.

The second aperture 20 b may be formed across the sacroiliac jointproximate to where the first aperture 20 a is formed in the sacroiliacjoint. The second aperture 20 b may be oriented at an angle so that thedistal end of the second screw is slightly anterior and superior to aproximal end of the second screw.

A variety of techniques may be used to determine the location at whichthe first aperture 20 a and the second aperture 20 b are to be formed inthe ilium as well as the orientation of the ilium so that the firstaperture 20 a and the second aperture 20 b may be in a desired positionand not result in damage to the tissue adjacent to and/or above wherethe first aperture 20 a and the second aperture 20 b are to be formed.

A non-limiting example of a technique that may be used to determine thelocation and orientation of the first aperture 20 a and second aperture20 b is a fluoroscope. To assist in evaluating the location andorientation of the anatomical structures proximate to where theundercutting system 10 will be used, it is possible to perform thefluoroscopic imaging from multiple directions.

One such direction for the fluoroscopic imaging is a lateral view acrossthe patient's pelvis. The lateral sacral view provides a visualizationof the starting point for the sacroiliac joint access by best showingcritical boundaries of the safe bony corridor such as the anteriorsacral cortex and the alar slope.

While less clear but also visible, the lateral sacral view provides theability to see the sacral neural foramina and the spinal canal. Thelateral view along with the outlet view can help to identify sacraldysmorphism, a challenging anatomical variation that could lead to apossible contraindication relating to the use of the undercuttingsystem.

The lateral view may be obtained by aligning the projections of the twogreater sciatic notches and the two iliac cortical densities. Tominimize the x-ray exposure, it is not necessary for there to be exactalignment of the preceding elements.

If the greater sciatic notches and the iliac cortical densities are notsimultaneously aligned, it is possible to split the difference betweenthese components. Alternatively, when alignment of the iliac corticaldensities is difficult, alignment of the greater sciatic notches may besufficient for performing the lateral fluoroscopic image.

It should also be noted that when aligning for the lateral view, truelateral of the sacrum may not appear to be true lateral to the patient.For the purposes of this invention, the important facture is thealignment of the sacrum.

Another view for the fluoroscopic imaging is an anteroposterior viewwith a caudal tilt. This view, which is referred to as the inlet view,may provide an excellent mediolateral view of the advancing guide pinand/or bone screw. This view also best enables avoidance of theposterior spinal canal and the anterior limit of the sacrum.

The inlet view is used in conjunction with the outlet view, which isdescribed below, while advancing the guide pin or bone screw mediallyinto the patient. Together the inlet view and the outlet view provideorthogonal images to guide screw insertion in all three dimensions.

The inlet view is obtained by tilting the fluoroscopic receiver caudalfrom the anteroposterior position. The device is aligned with a linecreated by the anterior-inferior sacral cortex and the iliac pelvic brimwith the second foramina. To minimize the x-ray exposure, it is notneeded for there to be perfect alignment of the inlet view.

Still another view of the fluoroscope imaging is an anteroposterior viewwith a cephalad tilt. This view, which is referred to as the outletview, may provide an excellent mediolateral view of the advancing guidepin and bone screw towards the center of the sacral body. The outletview enables avoidance of the Superior S1 end-plate and the S1neuroforamina.

The outlet view may be used in conjunction with the inlet view whileadvancing the guide pin or bone screw medially into the patient. Whenviewed together, the inlet view and the outlet view provide orthogonalimage to guide screw insertion in all three dimensions.

The outlet view is best suited for viewing the sacroiliac joint tofacilitate cartilage excision. While the outlet view may be similar to a“Judet” view, it is distinct from such a view and, as such, these viewsare not interchangeable.

The outlet view assure that the tip of the guide pin is cephalad to thesacral nerve foramen. The outlet view also distinguishes the cephaladborder of the sacrum, which is actually the posterior sacral alarregion. The anterior aspects of the sacral alar are sloped inferiorlyrelative to the posterior sacral alar region. The failure to account forthis forward sloping could result in the extraosseus screw placementbeing dangerously close to the iliac vessels and/or the fifth lumbarnerve root.

The outlet view may be obtained by tilting the fluoroscope receivercephalad from an anteroposterior position until the top of the symphysispubis is located at the S2 body. To minimize x-ray exposure, it is notneeded for there to be perfect alignment of the outlet view.

As an initial point in locating a location for access, a relativelysmall guide pin such as having a length of about 3 millimeters is heldto the outside of the patient proximate to the location of theiliosacral corridor. The tip of the guide pin may be positioned caudalto the iliac cortical density and cephalad to the interosseous path ofthe upper sacral nerve root.

The lateral projection of the iliosacral corridor identifies the safestposition for the distal end of the bone screw that is insertedlaterally. The proximal entry point may be outside the iliosacralcorridor.

The guide pin tip can be located within the midportion of the alar boneon the lateral image. The iliosacral corridor is the best location forpassage of the bone screw using in conjunction with the sacroiliacfusion.

After marking the skin, a vertical incision having a length of betweenabout 2 and 4 centimeter is formed in the skin. Next, using bluntdilation, a probe is extended through the tissue in line with the futurepath of the screw until reaching the ilium bone.

The most effective area for joint preparation may be theinferior-anterior edge of the safe zone closer to the articularcartilage portion of the joint as opposed to the interosseous portiondirectly lateral of the safe zone.

The articular portion of the joint is more flat, which is advantageousto encourage fusion at the articular portion of the sacroiliac joint. Incontrast, the interosseous portion of the joint, which is posterior tothe safe zone, is steeply angulated from perpendicular, and very lumpyand irregular.

Next, the undercutting system 10 is positioned in a retractedconfiguration so that the probe assembly 32 does not interfere with theinsertion process. The distal end of the undercutting system 10 isextended into the aperture 20, as illustrated in FIG. 31.

Once the distal end of the undercutting system 10 is positioned betweenthe ilium 14 and the sacrum 16, the probe assembly 32 is moved to an atleast partially extended configuration, as illustrated in FIG. 32.

The undercutting system 10 is rotated to so that the probe assembly 32causes a path to be defined between the ilium 14 and the sacrum 16. Bydefining the path using the probe assembly 32, the potential of thecutting assembly 132 digging too deeply into the ilium 14 or the sacrum16 is reduced.

Next, the cutting assembly 132 is slid over the probe assembly 32 untilthe cutting element 134 extends from the distal end of the insertionapparatus 30 and is positioned between the ilium 14 and the sacrum 16.The undercutting system 10 is rotated so that the cutting element 134contacts tissue between the ilium 14 and the sacrum 16 to cause suchtissue to be cut into pieces. Alternatively or additionally, the cuttingelement 134 may cause cartilage and/or tissue to be scraped from thesurface of at least one of the ilium 14 and the sacrum 16. If it isdesired to prepare a region having a larger diameter, the cuttingassembly 132 may be advanced further and then the undercutting system 10may be rotated.

Depending on a variety of factors such as the sharpness of the cuttingassembly 32 and the hardness of the material being cut, it may not bepossible to merely cut through the cartilage and bone using just arotational motion. Rather, it may be necessary to alternate rotating theundercutting system in clockwise and counter clockwise directions toincrease the area that is prepared. The control knob can be periodicallyrotated to cause the cutting assembly 32 to extend progressively furtherfrom the undercutting system 10. While in many circumstances, it may bedesirable to prepare a circular area, it is also possible to use theconcepts of the invention to prepare a semi-circular area.

Alternatively or additionally, the probe assembly 32 may be withdrawnand a cutting assembly such as is illustrated in FIGS. 21-25 may be usedto cut tissue in the region between the ilium 14 and the sacrum 16 thathas been defined by the probe assembly 32.

Contact between the cutting assembly 132 and the inner surfaces of theilium 14 and the sacrum 16 causes the respective surfaces to be abradedto create bleeding bone, which may be desirable to facilitate bonegrowth between the ilium 14 and the sacrum 16 as part of the sacroiliacfusion process.

A variety of techniques may be used to evaluate the amount of cartilagethat has been removed and the extent to which the surfaces of the iliumand the sacrum have been prepared. Examples of such suitable techniquesinclude monitoring the sound emitted during the cutting process, as thecutting of bone may make a scraping sound.

The person operating the undercutting system may monitor the performanceof the process using the feel of the cutting head, as it may be moredifficult for the cutting head to cut through the ilium and the sacrumthan the cartilage.

It is also possible to monitor the progress of the preparation for thesacroiliac fusion using a fluoroscope. While these techniques aredescribed individually, it is possible for one or more of the precedingtechniques to be combined.

In certain embodiments, the bits of cartilage and other tissue frombetween the ilium 14 and the sacrum 16 may become caught in the cuttingassembly during the cutting process. In such a situation, the cartilageand other tissue are removed from between the ilium 14 and the sacrum 16when the cutting assembly is retracted.

It may be necessary to clean the cutting assembly and then reinsert thecutting assembly into the region between the ilium 14 and the sacrum 16to remove additional bits of the cartilage and other tissue.

Alternatively or additionally, a technique may be utilized to remove thebits of cartilage and other tissue from between the ilium 14 and thesacrum 16. One suitable apparatus that may be used for remove the bitsof cartilage and other tissue is a radial deployment surgical tool,which is described in U.S. application Ser. No. 12/941,763, which wasfiled with the U.S. Patent & Trademark Office on Nov. 8, 2010, and whichis assigned to the assignee of the present patent application.

Another technique for removing the cut up bits of cartilage is to flushthe region with a fluid and then suction out the water with the cut upbits of cartilage. The process may be repeated until a desired amount ofthe cut up bits of cartilage is removed from between the ilium and thesacrum.

After the surfaces of the ilium and the sacrum have been prepared, abone graft may be inserted. Then, a variety of techniques may be used tomaintain the ilium and the sacrum in a fixed position with respect toeach other. Examples of suitable fixation techniques include bonescrews, cannulated screws, pins, cages, glue, coupled device with balland socket and Herbert screws.

Thereafter, bone screws 720 may be inserted into each of the apertures20, as illustrated in FIG. 33. The bone screws 620 will be effective atmaintaining the ilium 14 and the sacrum 16 in a stationary position withrespect to each other as bone grows between the ilium 14 and the sacrum16 to cause fusion of the ilium 14 and the sacrum 16.

In certain embodiments, the orientation of each of the apertures 20 maybe generally parallel to each other. In other embodiments, the apertures20 may be formed in a non-parallel relationship.

For example, the two screws 720 on each side converge toward the safezone as illustrated in FIGS. 34-38, which are lateral, inlet and outletfluoroscopic images of the pelvis region. It is to be noted that neitherof the bone screws 720 penetrate into the alar scope, which could becaused by the entry point being too cephalad. Such a situation is to beavoided because it can result in complications to the patient, whichrequires immediate correction.

While the figures only illustrated the procedure being performed on oneside of the patient, a person of skill in the art will appreciate thatthe process may be repeated on the other side of the patient.

While the concepts of the invention are primarily described inconjunction with preparation for a sacroiliac fusion, a person of skillin the art will appreciate that the concepts may be adapted for otherjoints in the body. The concepts may also be used for preparing aninterior region of a bone.

As an alternative to disturbing the surfaces of the ilium 14 and thesacrum 16 to expose bleeding bone, it is possible for the undercuttingsystem to remove more bone from at least one of the ilium 14 and thesacrum 16. Such a process could create a relatively planar preparedregion between the ilium 14 and the sacrum 16. Because the ilium 14 andthe sacrum 16 are not substantially flat, a greater amount of bone maybe removed using such a process. This process obliterates a portion ofat least one of the ilium 14 and the sacrum 16.

However, when performing such a process, care should be exercised sothat the cutting assembly does not cut all the way through the ilium 14or the sacrum 16. Additionally, care should be exercised to not removetoo much of the ilium 14 or the sacrum 16 as such a process could resultin weakening of the ilium 14 or the sacrum 16.

The process associated with this embodiment may require the use of asharper and/or stronger cutting assembly so that the cutting assemblyresists damage when forces needed to cut more deeply into the ilium 14and sacrum 16 are used.

After the fusion region is prepared, the cut up bone, cartilage andother tissue may be removed from the fusion region using one of theprocesses described in the other portions of this patent application. Abone growth material may be placed into the fusion region. A bone screwor other fastening device may be used to retain the ilium 14 and thesacrum 16 in a stationary position with respect to each other while bonegrows between the ilium 14 and the sacrum 16.

While the concepts of the invention are primarily described inconjunction with preparation for a sacroiliac fusion, a person of skillin the art will appreciate that the concepts may be adapted for otherjoints in the body. The concepts may also be used for preparing aninterior region of a bone.

In the preceding detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thepreceding detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is contemplated that features disclosed in this application, as wellas those described in the above applications incorporated by reference,can be mixed and matched to suit particular circumstances. Various othermodifications and changes will be apparent to those of ordinary skill.

1. A method of performing an orthopedic procedure in the sacroiliacregion, the method comprising: forming at least one aperture that atleast partially extends through at least one of an ilium and a sacrum;inserting an undercutting system at least partially into the aperture,wherein the undercutting system comprises an insertion apparatus, aprobe assembly and a cutting assembly; moving the probe assembly withrespect to the insertion apparatus from a retracted position to anextended position, wherein when in the retracted position, the probeassembly is substantially within the insertion apparatus and whereinwhen in the extended position, at least a portion of the probe assemblyextends from the insertion apparatus; manipulating the probe assemblywithin a joint between the ilium and the sacrum while the probe assemblyis in the extended position; moving the cutting assembly with respect tothe insertion apparatus from a retracted position to an extendedposition, wherein when in the retracted position, the cutting assemblyis substantially within the insertion apparatus and wherein when in theextended position, at least a portion of the cutting assembly extendsfrom the insertion apparatus, wherein the cutting assembly is sharperthan the probe assembly; manipulating the cutting assembly within thejoint between the ilium and the sacrum while the cutting assembly is inthe extended position to form a fusion region; and removing theundercutting system from the aperture.
 2. The method of claim 1, whereinthe aperture is oriented at an angle of between about 45° and 135° withrespect to the at least one of the ilium and the sacrum through whichthe aperture extends.
 3. The method of claim 1, wherein the insertionapparatus is oriented about a central axis and wherein as the cuttingassembly moves to the extended position, a distal end of the cuttingassembly moves away from the central axis.
 4. The method of claim 1,wherein forming the fusion region comprises removing at least a portionof a surface of the ilium and the sacrum with the cutting assembly toproduce bleeding bone.
 5. The method of claim 1, wherein the cuttingassembly extends over at least a portion of the probe assembly.
 6. Themethod of claim 1, wherein the cutting assembly has a cutting surface onat least one edge thereof, wherein the cutting assembly comprises afirst cutting assembly and a second cutting assembly, wherein the secondcutting assembly has a height that is greater than a height of the firstcutting assembly and wherein forming the fusion region comprises:positioning the first cutting assembly between the ilium and the sacrum;moving the first cutting assembly between the ilium and the sacrum tocut tissue; positioning the second cutting assembly between the iliumand the sacrum; and moving the second cutting assembly between the iliumand the sacrum to cut tissue.
 7. The method of claim 1, and furthercomprising retaining the sacrum in the stationary position with respectto the ilium by inserting a fastening device into the aperture so thatthe fastening device engages the ilium and the sacrum, wherein thefastening device is a screw, a peg, a pin, a cage, glue or a coupleddevice having a ball and a socket.
 8. The method of claim 1, wherein thecutting assembly resists movement in a radial direction with respect tothe insertion apparatus and wherein the cutting assembly exhibitsflexibility in a distal-proximal direction with respect to the insertionapparatus.
 9. The method of claim 1, and further comprising a cuttingassembly locking mechanism that is movable between a lockedconfiguration and an unlocked configuration, wherein the cuttingassembly is retained in a stationary position with respect to theinsertion apparatus when the cutting assembly lock mechanism is in thelocked configuration and wherein the cutting assembly is rotatable withrespect to the insertion apparatus when the cutting assembly lockmechanism is in the unlocked configuration.
 10. The method of claim 1,wherein the insertion apparatus further comprises a control portionoperably attached thereto proximate a proximal end thereof and whereinthe control portion is operably attached to the cutting assembly formoving the probe assembly and the cutting assembly between the extendedconfiguration and the refracted configuration.
 11. The method of claim1, and further comprising removing tissue cut with the cutting assemblyfrom the fusion region.
 12. A method of performing an orthopedicprocedure in the sacroiliac region, the method comprising: forming atleast one aperture that at least partially extends through at least oneof an ilium and a sacrum; inserting an undercutting system at leastpartially into the aperture, wherein the undercutting system comprises acutting assembly; moving the cutting assembly to an extended positionbetween the ilium and the sacrum where a portion of the cutting assemblyextends beyond an outer periphery of the undercutting system; forming afusion region by moving the cutting assembly between the ilium and thesacrum; moving the cutting assembly to a retracted position where thecutting assembly is substantially within the outer periphery of theundercutting system; removing the undercutting system from the aperture;and inserting a fastening device into the ilium aperture and the sacrumaperture, wherein the fastening device retains the ilium and the sacrumin a stationary position with respect to each other.
 13. The method ofclaim 12, wherein the aperture is oriented at an angle of between about45° and 135° with respect to the at least one of the ilium and thesacrum through which the aperture extends.
 14. The method of claim 12,wherein proximate a distal end of the undercutting system, theundercutting system is oriented about a central axis and wherein as thecutting assembly moves to the extended position, a distal end of thecutting assembly moves away from the central axis.
 15. The method ofclaim 12, wherein forming the fusion region comprises removing at leasta portion of a surface of the ilium and the sacrum with the cuttingassembly to produce bleeding bone.
 16. The method of claim 12, whereinthe cutting assembly comprises a first cutting assembly and a secondcutting assembly and wherein forming the fusion region comprises: movingthe first cutting assembly between the ilium and the sacrum to cuttissue; and moving the second cutting assembly between the ilium and thesacrum to cut tissue, wherein the second cutting assembly extends overat least a portion of the first cutting assembly, wherein the secondcutting assembly is sharper than the first cutting assembly and whereinthe second cutting assembly has a height that is greater than a heightof the first cutting assembly.
 17. The method of claim 16, wherein:moving the first cutting assembly between the ilium and the sacrumcauses the first cutting assembly to extend into an intra-articularregion between the ilium and the sacrum; and moving the second cuttingassembly between the ilium and the sacrum comprises: cutting tissuebetween the ilium and the sacrum; and removing at least a portion of asurface of the ilium and the sacrum to produce bleeding bone.
 18. Themethod of claim 12, wherein the fastening device is a screw, a peg, apin, a cage, glue or a coupled device having a ball and a socket andwherein the fastening device is the same as the first fastening device.19. The method of claim 12, wherein the undercutting system furthercomprises an insertion apparatus and wherein the cutting assembly isoperably attached to the insertion apparatus.
 20. The method of claim19, wherein the undercutting system further comprises a cutting assemblylocking mechanism, wherein the cutting assembly locking mechanism ismovable between a locked configuration and an unlocked configuration,wherein the cutting assembly is retained in a stationary position withrespect to the insertion apparatus when the cutting assembly lockmechanism is in the locked configuration and wherein the cuttingassembly is rotatable with respect to the insertion apparatus when thecutting assembly lock mechanism is in the unlocked configuration. 21.The method of claim 19, wherein the insertion apparatus furthercomprises a control portion operably attached thereto proximate aproximal end thereof and wherein the control portion is operablyattached to the cutting assembly for moving the cutting assembly betweenthe extended configuration and the retracted configuration.